Elderly Athlon X2 4200+

My Athlon 64 X2 system's always been a little bit unstable, but recently I've been trying to play some new games and it's become intolerable! The spec is:

* Athlon 64 X2 4200+ (Socket 939)
* Asus Silent Geforce 7600GS AGP
* 1 GB RAM in dual channel configuration
* MSI K8N Neo2 Platinum motherboard
* Akasa AK-856 cooler
* 2 x SATA hard drives
* Generic DVD-RW
* Windows XP Pro

Basically the system is reasonably stable in normal usage, but after playing various 3D games it reboots / the graphics freezes with the mouse cursor active although for different games it takes different times (Halflife 2 = 30 mins, Fallout 3 = 30 mins, Left 4 Dead demo = on menu screen, C & C 3 = 5 minutes, Redalert 3 = several hours) which is weird as there doesn't seem to be any correlation with graphic intensiveness.

I think there are 3 likely suspect:

* CPU overheating - This CPU has always run very hot(60 degrees idle according to the MSI hardware monitor) even after applying arctic silver and I don't know why - Is the Akasa cooler not powerful enough for this CPU or does this suggest some other problem?

* GPU overheating - Are the passive coolers on these Asus cards generally ok and if not are they reasonably easily replacable? Also what's a good well to tell GPU temperature?

* PSU - I can't rememeber what power the PSU is, but what do you think the minimum rating to use for this system should be?

I suspect the problems are related to the CPU or the GPU as they're the latest additions, but if anyone has any other ideas I'd be more than happy to investigate. It's obviously not a high (or even mid) range pc anymore but before it crashes it plays the games I want and is pretty quick in windows so I'm not overly keen on upgrading(especially as everything'd need to be replaced)

Cheers

Jamie