Check all the connections, try pulling them out and reconnecting them again.
I'm just looking at the specs in your signature, and that computer is really dated, and some of the parts, namely the CD drive, may be on their last leg.
I wouldn't be too concerned, Cd drives cost like 10 bucks tops, so replacing it shouldn't be a problem.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w