Pls try the following. Hope it helps you.
If u are sure the drive is well connected and jumpers set correctly, run the "system restore" utility. Restore the system to an earlier date when the drive last work.
I also have the experience that whenever PC DJ is running, Cds dont open, therefore a recently installed application may be causing the problem. Unistall any new program u installed.
I hope the system restore help You if only the problem is not from the drive itself.