DVD rom safe mode only

ok so to start off with i am a tech, and a fairly good one but i dont know if i am just over looking something or if there is just something wrong in general.

The problem:

I installed an asus cd /dvd rw drive in a customers desktop.
it is a dell dimension 2400. running xp with all the updates.

the drive works in safe mode. i can swap cd's and dvds and the names and files all appear like normal.

however in standard boot, if there is a dvd or cd in the drive when it boots up then that one particular disk works fine. switch disks however and nothing appears in the drive. if i right click and go to properties 50% of the time it will recognize the disk and work correctly.

there are no virus' that i have been able to find, no upper or lower limits, the drive is not set to cable select it is a true master drive. i have stopped all services as well as start up programs nothing seems to help the situation.

any help with this would be awesome i have been hammering on this thing for a week and a half like a drunken monkey. the customer wants it back soon and i am lost

thanks in advance for any advice

LOL Dragon this is going to be tricky one as you have already run through al the troubleshooting i would recommend including the checks on the upper and lower filters. Still possibly a virus or some sort of malware. I use Kaspersky Internet Security along with Malwarebytes, not sure if you want t give those two a shot i have used these as recommended programs all through my IT career. Couldn't hurt to try i always say...a bit time consuming however =)