System Crashing, Help needed!

[CTMF92]

I'll jump straight to the point, my computer crashes when I play games for a certain period of time, an example would be Half Life 2 on medium settings will crash after about 2 hours or less and I think it may have to do with the temperature of the PC. I've tried many solutions including Replacing the heatsink on the CPU, backdating drivers on my GPU, cleaning and re-applying thermal paste onto my CPU moving the computer to a more ventilated area, having the lid off and a powerful fan blowing onto the motherboard and upgrapding the PSU, making the GPU Fan run at highest speed possible and to always run for best performance.

If I were to leave the PC idle on my desktop the temp of the GPU will sit at around 30-35C, after running WoW on Medium-High settings the GPU temp will rise to about 50C and can go much higher and Ive checked the core temps using the SIW program and when the GPU was at 50C Core 1 was at 89C, after about 2-4 hours it will crash and the likelyness that it will crash increases if I am multi tasking on the PC (Gaming and Browsing)

The way the PC crashes is just an immediate shutdown as it the plug was turned off at the wall.

Computer Specs
AMD FX 4100 3.60 Ghz CPU
Windows 7 Ultimate 32bit (Upgrading to Win 8 64bit in a few days) will this make a huge difference?
8gb Corsair DDR3 RAM
Arctic 13 Freezer Heatsink
Asus GT 440 1gb DDR5 Gfx Card
I believe the motherboard is an Asus M5A78L.

any help would be greatly appreciated thanks.

 

[nna2]

89C is a bit excessive for a CPU, and is high for a lower end GPU

make sure your cooler is screwed all the way down, try running the original cooler if you can't get cooler temps with your current one

 

[CTMF92]

I reseated the heatsink and made sure it was fitted properly but was still very high in temp, so I've reverted back to the original cooler to see if it helps.