I suspect a faulty power supply, since this issue seems to always occur when the CD drive is being used. It means more power is being pulled from the power supply and it can't handle the load anymore. Having a local computer store test your power supply is a good idea.
You could have reinstalled windows from a bootable CD... but I guess it's too late to worry about that now.
Anyway, with a 5 year old pc the thing might just be tired sometimes you have no choice but to get yourself a new computer. I had a computer that behaved similarly to the one you've got now and in the end I had to start from scratch because the motherboard was just shot.
Cooler Master HAF 922 case
Thermaltake 750 watt modular psu
MSI P67A-C43 board
8 GB Corsair XMS DDR3 1300
Intel core i5 Sandy Bridge quad core@ 3.3 ghz
MSI GTX 570
WD 2 TB HDD
64-bit Windows 7
Rosewill USB Wirless Adapter
LG Blu-Ray DVD Combo Drive
I'm a PC!