> One other possibility is that during the DVD drive install, the IDE
> cable may have ben slightly "disconnected" from the secondary IDE
> port. Re-open the Dell PC and check all cables.

I just re-checked that, and everything is properly connected.
Actually, i don't think that would be it because when i disable my
IDE, on first reboot, the IDE comes on as recognized, and the DVD
drive as well but only in device manager, though it remains
inaccessible by the system (and on further reboots, that's when the
IDE comes disabled, and then of course, no DVD drive is recognized
whatsoever). that tells me the connection is good, and the IDE cable
is working. otherwise nothing would change.

> Dell they are normally CS (Cable Select) - and have you
> asked Dell Support about this?

Yes i asked Dell support and both my old drive and new one are on CS.
However, i played around with settings, just to make sure, and none
work, so i left it as CS.

Thank you guys for your help and suggestions by the way !