PC keeps turning off?

[Linken]

Need some help figuring out what the problem might be.

First off, specs are:

Intel Core 2 Duo E6600 "LGA775 Conroe" 2.40GHz (1066FSB) - Retail
OcUK GeForce 8800 GTS 320MB GDDR3 HDTV/Dual DVI (PCI-Express) - Retail
Corsair HX 520W ATX2.2 Modular SLI Compliant PSU (CMPSU-520HXUK)
Seagate Barracuda 7200.10 320GB ST3320620AS SATA-II 16MB Cache - OEM
Lian-Li PC-7 PLUS Aluminium Midi-Tower Case - Silver
Gigabyte GA_P35C_DS3R (Socket 775) PCI-Express DDR2 & DDR3 Motherboard
Crucial Ballistix 2GB (2x1GB) DDR2 PC2-5300C3 667MHz Dual Channel Kit (BL2KIT12864AA663)

I've had this PC about a week, haven't done much OCing to it. I raised the FSB up to 304, and turned off the option in BIOS that limits your CPU when not under load. And today when I was just watching a video, nothing else it shut down on me, really weird. So I open it up to see if I can see any obvious errors, didn't see anything so I put it back together and plug everything back in and..it boots. I had no sound when I booted it back up which was weird and then it shut down again after about 5 minutes, I also changed the FSB down to 290 before I loaded it back up.

Any ideas? Off to try and boot it again!

 

[Cyber-Mav]

overheating cpu or dodgey mamory. first step is to check temps, if thier fine then run memtest.

 

[Linken]

Okay, I have set everything back to stock and it hasn't shut down yet.. I have no idea what was causing it, temps were at around 41c idle before I changed it back to stock.