The CD-ROM drive cannot be recognized or seen by the system, or the CD-ROM driver hangs or says it cannot find the CD-ROM when it loads

The CD-ROM drive cannot be recognized or seen by the system, or the CD-ROM driver hangs or says it cannot find the CD-ROM when it loads

Explanation: You cannot access the CD-ROM. It is not being recognized by the system and so is not usable. This usually manifests itself as an error message or lockup produced by a CD-ROM driver at boot time, or getting an "Invalid drive specification error" trying to reference the drive.

Diagnosis: There are a wide variety of causes for a CD-ROM drive that does not register with the system. Most fall into the usual two categories: incorrect configuration, and hardware problems or incompatibility.

Recommendation: You may find that the problem is actually more than one of the following, but try them one at a time first:

Check the power to the CD-ROM drive first. See if the activity LED works. Try to open the tray. If the tray doesn't open the drive does not have power; check the plug connection to the drive inside the case. If it doesn't work, try another one. If you can't get power to the drive, it is most likely dead and needs to be repaired or replaced. If you have intermittent power problems or problems with other devices as well, the power supply could be a problem.
If the CD-ROM works in Windows 95 but does not work when you "restart in MS-DOS mode", then you have a relatively simple system file configuration problem. See here for a solution.
If you have recently installed this drive, or have worked in the system case recently, consult this troubleshooting list of common problems.
If you have another system that you can try the drive in, it is a good idea to connect it to the other PC and see if it will be detected there. Bear in mind that moving the drive to a new PC can introduce other variables that might confuse the issue, but I have seen this be a very effective way to isolate the trouble to either the CD-ROM drive or the PC it is installed into. Similarly, if you try another identical (or even just similar) CD-ROM in place of the one not working, that can tell you if the problem is the drive or the drive interface.
If you have a DOS CD-ROM driver in your CONFIG.SYS file, check to make sure that it has the correct parameters. If you recently moved the drive to a different IDE channel or changed it from master to slave or vice-versa, you may need to change the command that invokes the driver. Look here for more.
On some systems, loading the CD-ROM driver in CONFIG.SYS will cause conflicts with other IDE devices. This will cause the CD-ROM drive not to be found within Windows 95. If this happens, try temporarily removing the CD-ROM driver command from CONFIG.SYS and see if Windows 95 now sees the device. If it does, you should leave the line out of CONFIG.SYS permanently. This will mean you cannot access the CD-ROM under DOS any more, but there is a workaround: creating a custom boot profile for DOS programs. See here for more.
If you are using the drive in DOS (or Windows 3.x, or Windows 95 MS-DOS mode), you must have a CD-ROM driver in your CONFIG.SYS, and you must run MSCDEX to create the drive letter for the drive (usually it is in AUTOEXEC.BAT; sometimes it is in DOSSTART.BAT in the Windows directory, in Windows 95). You must make sure that you use the right driver for your drive (it should come with an install program on a floppy that will take care of everything).
If using a DOS driver and MSCDEX, and you are encountering errors with MSCDEX, refer to this section.
If you are connecting an older CD-ROM drive, especially one that is 2X speed or slower, there is a good chance that it uses a proprietary interface, not standard ATAPI/IDE. These drives use a connector and cable that looks much like standard IDE, so it is easy to confuse them. In most cases these will work off the special ports on some sound cards (since they were originally sold as part of multimedia kits) but in some cases they require special dedicated controllers. Make sure to read your product documentation. (There are some real IDE/ATAPI 2X drives, by the way.)
If the drive is SCSI, you need to check all of the various parts of the SCSI chain. The SCSI host adapter (controller) must be checked to ensure that it is working properly. The CD-ROM drive and all other devices on the SCSI chain must have a different device ID. The termination must be set up correctly. See here for more details on SCSI configuration.
If the drive is on an IDE channel with another drive (hard disk or CD-ROM), then you should try the disk by itself on the channel to eliminate the possibility of conflict. You may need to change the jumpers on the drive to do this, but you definitely need to try the drive without the complicating factor of another device on the channel. If the disk works by itself but not when set up with another drive, you may have a master/slave conflict; see this section in the hard disk area for ideas on fixing these problems (the general guidelines are the same for CD-ROM drives.) Note that some drives may not work by themselves on a channel so don't assume that this means the drive is bad.
Beware of some CD-ROMs that will not work by themselves on an IDE channel if bus mastering drivers have been installed for the hard disks.
Some CD-ROMs will only work on an IDE channel by themselves if they are jumpered as master (this is the "correct" way to jumper them, but some drives will work as solo slaves on a channel, others will not.)
Make sure that the CD-ROM drive is configured properly. The jumpers should be set correctly. The ribbon cable should be inserted properly and pin 1 on the drive should be matched up with pin 1 on the interface controller or motherboard.
If you had a master and a slave drive on the IDE channel and removed one of the two drives, the one that remains may need to be rejumpered. Similarly, if you add another drive to the channel the first one there may need to be changed, even if you are adding a slave to an existing drive. Some hard disks--for example those manufactured by Western Digital--use different jumpers for when they are a master with a slave drive present vs. when they are alone on a channel.
Make sure that the IDE controller is enabled if you are using an ATAPI/IDE drive; on modern systems the IDE controllers are enabled or disabled using BIOS settings. It is common for the secondary controller to be disabled; if you are adding a CD-ROM to the secondary channel you will need to enable the channel.
Some hard disks do not like having CD-ROMs attached to them as slaves, in general. You should try the CD-ROM on a different channel (again, isolate the problem by seeing if the drive works by itself on a channel, bearing in mind that some won't).
If the drive isn't recognized by itself on one channel, try another and see if the problem is fixed. If so, this implies that the original IDE channel is misconfigured in some way. There may be a resource conflict or other problem with the channel. This is especially true if you have the unit on a tertiary controller, for example one found on a sound card.
Tertiary IDE controllers, such as those found on sound cards, often do not work with bus mastering IDE drivers installed. See here for more on bus mastering driver problems.
An IDE cable that is too long can cause permanent or intermittent problems with drives. Make sure the cable is not longer than the nominal 18" limit. Try an even shorter cable if problems ensue.
If another similar CD-ROM drive is available, try replacing the CD-ROM drive with this one (you can just leave it loose and move the power and interface cables while testing, if you are careful). You may need to change the driver that is loaded in CONFIG.SYS if you use a different manufacturer's drive. See if the problem goes away. If it does the drive may be bad; otherwise the interface is implicated.
Another test to isolate a problem to the drive or the interface is to try a hard disk in the position where the CD-ROM drive was. If the hard drive works but the CD-ROM does not then that tells you that either the CD-ROM is bad or there is a compatibility problem between the interface and the CD-ROM drive.
Watch out for 32-bit disk access being enabled under Windows 3.x. This may cause problems with CD-ROM drives on the ATAPI/IDE interface.
Systems with dynamic drive overlays installed to allow use of larger hard disks may not be too impressed if you put a CD-ROM on the same channel as the hard disk. I have seen systems refuse to boot under these circumstances.

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