cdrom missing sometimes

Edited text of question

Are you using bus mastering drivers?  Some cdroms can not use bus mastering.  Also some cdroms require the realmode driver to be loaded from the config.sys?  Let us know.

Thanks

graceco,
What is your operating system?
Is your CDROM an IDE or SCSI device?
Any error messages at bootup?
Can you get the error to repeat itself somehow? (Power-on or warm boot, CD inserted or not, etc.)
Please post your autoexec.bat & config.sys files here so we may determine if they contain the problem.
Regards,
Ralph

Is any difference between bootup CD-ROM presence and non-presence ?
My Infra-18oo ALWAYS detected when no CD inside upon bootup and
50/50 chances that not detected when CD-ROM inside and boot is
cold. Creative supported my guess that problem is bad firmware
code. Maybe you have exactly same case here ?

maybe the cables are lost
happens to me sometimes

Edited text of question

Edited text of question

Right-click on MyComputer -> Properties -> DeviceManager tab
Locate Hard Drive controllers branch and expand it by clicking on
'+'. If you have entries like 82371xB blah, blah blah ... (where
x is A, S or F) and then Primary IDE (dual fifo) then you have
bus mastering drivers installed.

graceco,
You do not have to edit your question every time in order to respond to our comments.
Simply type your responses into the box at the bottom of the page and then click submit button.

The model number you have supplied for the CDROM is not listed at the Diamond Data (Mitsubishi) site, here:
http://www.mitsubishi-electric.com.au/index.asp
Do you have the Dos real mode driver for the CDROM?
Ralph

It is likely that the lens on your CD-ROM drive has dust on it.  If your drive is getting old or if it has been a long time since you've cleaned the lens, it may be a little dusty or possibly even damaged.  DO NOT try to clean the lens manually because you will destroy your CD-ROM drive.  You can take it to a shop or buy a CD-ROM drive cleaning kit.  Hope this helps.

Thankyou for lense clean suggestion but been there done.. I very much doubt that the computer would not see the cdrom as connected if the lense was a bit dirty.But I may be wrong. In response to some of the other comments I need to find the right drivers to put in the config/autoexec. And yes I do have mastering. At the end of the day I may need to get a new cdrom. From memory the problem started to occur after changing to an AOPEN AP5T motherboard which I installed myself.Sorry can not remember previous board.Many thanks for help.

Did you repeat the cabling on the old m/b or is the drive rigged up differently this time? Is the jumpering correct?

Ralph and Sircaleb, I have a problem. Sircalebs answer, though at first reading seeming very unlikely and I apologise for rejecting it off hand, now appears to have worked. After cleaning with a lense cleaning disk I have not yet encountered a failure on bootup. Yet I also appreciate your efforts Ralph and don't want to reject your answer either.So I have accepted your answer Ralph. I will submit another with Sircaleb answer only on it for the other 55. Grant

Thanks, Grant.
I'm glad you got it working!
Regards,
Ralph