My PC is Mount Vesuvius. Overheating problems.
 

Ok so here's what my PC has been doing:
I turn it on log in to windows, everything loads annoyingly slow, CoreTemp tells me my CPU is at 60c when idle. After about 2 mins(sometimes more sometimes less) it locks up, doesnt shut down. I've left it like that for about 10 - 15 mins to see if it'll recover but it doesnt. I'm assuming this is caused by over heating but I dont know why its so damn hot. Bios settings are at default, it isnt being overclocked. Also when a PC overheats...doesnt it normally shutdown to save itself? rather than lockup.
Oh and my household tempatures have gone down since the last time my PC was in working order because I moved to a place with better cooling.

My PC - Intel Core 2 - 2.4GHz
x2 1GB sticks of DDR ram
x2 250GB WD HDDs (one is sata the other is IDE)
x2 GeForce 7900 GTX viceo card
Antec 550w power supply
Asus p5n32 - sli se deluxe mobo
2 fans on the back, 1 front fan and one side fan.

PC history - Bought it about a year ago, had a friend build it. It ran great until
last May when the Mobo just died(sent it to Asus and got a new
one back) I rebuilt it, reapplied thermal paste and only put one
of the 2 video cards in(the other is being used by another PC)
and now it runs like crap and locks up.

Anything anyone can think of checking/changing/doing to help whip this bitch?

Also: Asus tech support is shit.

60°C is definitely at the upper tolerance of the Core 2 Duo.

Re-apply the thermal paste, making sure you clean off both the heatspreader on the CPU and the bottom surface of the heatsink as best as you can using a high-purity Isopropyl alcohol and a lint-free cloth (microfiber or a coffee filter).

When you apply the thermal compound, the orientation of the processor as you apply can make a big difference with the Core 2 Duos. When looking at the processor oriented such that the small triangle on it appears in the lower left, the two cores are arranged vertically in the center of the heat spreader. That is the most important place to apply the compound rather than worrying about corner-to-corner coverage. Most of the thermal energy is going to come strait up out of the cores through the head spreader, and you need a good thermal interface there to conduct the heat into the heatsink.