Australia huh? So that means in all likelihood there is a lot of dust, just like here :P Check the heat grills and/or fan(s) first.

Regardless, that is exactly how my gpu started dying - random resets (can't remember whether it was a complete shutdown or a reset each time). I tried everything, hoping it wasn't the expensive gpu including trying all possible ram combinations, in case it was a motherboard/ram issue. In the end however, replacing the gpu fixed it.

Yes good idea... a backup video card or another computer until it's fixed... you don't need the computer starting on fire.... or causing permanent damage...

Although if it is permanently damaged... Might check out newegg and look for openbox items for video cards, got my sapphire there and it works pretty well at good discount...

About the new thermal compound, it's important not to use much. (After removing the old paste properly with a bit of cleaning alcohol.)
Sometimes it's forgotten that the surfaces need a certain pressure for it to conduct the heat better, and it really put the compound in places it should be. Don't overtighten to crush the processor ofcourse, but evenly tighten it with all screws until it's tight. It may seem simple, but some efforts have different results. And it's never wondered why.

Right, and whatever you do, don't do this. http://zarobian.blog.com/files/2012/10/Features_Thermal-Paste-System-Builder.jpg

Yeah, cleaning the fans alone doesn't do much good in my case (well, it's of course necessary but it's not enough). The real dirt is usually stuck in the gaps in the heat sink for me. I don't know what your graphics card looks like but I have to disassemble mine to some degree to reach the spots where most of the dust gets stuck.

Ninja'ed, asked about the fans working...

Just back now, turned everything off, took out the card and thoroughly cleaned the gpu fan of dust (though their didn't seem to be THAT much in it and it seems to be spinning fine)..... and put it back in and just tried some games and..... same problem, still 90+ degrees...

I dunno I might just replace it, I don't think a standard 2GB card is that expensive anymore

FYI vacuum cleaner is not a good idea for GPU and CPU as there is a risk of bending stuff and it lacks focus (fine for the casing though)
A can of compressed air cost a few bucks and do wonders.

Yeah but my other parts are fine cooling wise, even the motherboard rarely goes above 50 and the hard-drives and CPU are in the 30-40 range, it's only the GPU getting overheated....

This thread reminded me to look after my computer aswell. Even though it is suffering problems so far:

Like for one I am unable to uninstall GOG games becasue, lets just say I caught a virus so I decided to "delete" it from the registry editor and for Uninstalling GOG it says Registry is unavaliable. So now in order for me to delete a GOG game I have to delete everything related to the game, the folders, the programs, the shortcuts, etc.

Also another problem is my Control Panal>System and Security>System does not show what my Processor is. (I know have a GTX 650)

Yeah, it's the exact same thing for me. I haven't had to clean my CPU even once (although I did, just to be safe) but my graphics card keeps catching tons of dirt. Don't know why that is exactly.

Wow 100 degrees and I was going to replace mine because it's running at a steady 60-80 degrees these days which makes the fan way too loud for my liking. But yes, cleaning the card could get you down a couple of degrees.

I'll prob do this tomorrow, think I still have some left over from my cpu
60-70 is normal (green) for a gpu according to speccy

Here's a neat study I found regarding thermal paste:
http://www.hardwaresecrets.com/printpage/What-is-the-Best-Way-to-Apply-Thermal-Grease-Part-1/1303

It's for CPUs, but I believe the same applies for GPUs.