[Solved] Home built pc lock up issue

hello all i need some serious help i recently built my first pc last month and i have been having
a issue with my pc locking up but it does not lock up at random times. but when i play a game or
trying to burn a DVD.... but i can burn CD's with no problem and also when i try and watch a blu ray
movie it locks up as well, when im watching a regular DVD it can play the whole movie with no problems.
I can leave the pc running all day long and surf the internet and it will not lock up at all
these is all the hardware from my PC everything is new except for the harddrive i got it from a co-worker,
but the hard drive was still wrapped up and was never open.

power supply:ultra X3 850w
DVD player: lite on 6X blu ray
ultra usb 2.0 md3 5.25 multi function panel
case: ultra m998 mid tower
ram: OZC reaper 4096MB pc10666 ddr3 1333Mhz (2x2048)
motherboard:evga nForce 790i ultra SLI socket 775
CPU:intel core 2 quad Q9650 3ghz 12mb 1333 fsb cpu
video card:bfg geforce gtx 285 oc 1gb PCIe b edition
HArd drive:seagate barracuda 1tb 32 mb sata hd
operating system: windows vista ultimate 32-bit

any advice would be helpful. thanks all in advance

I have some good news I found it's not my video card but my CPU
was overheating... Brought a new fan and some thermal compound
but it's still reading high temps at idle any advice for me
before new fan and compound
CPU 54c 129f
board 35c 98f

after new fan compound
CPU 50c 122f
board still the same