my friends comp does sort of the same thing except it makes a humming noise and turns off for 20 minutes, think it could be something to do with his ddr ram.
If you've been fuxin' with the heatsink or cpu fan it might be that there is a small gap between the heatsink and the processor. If that's the case then that would explain why ur bios is saying ur cpu is up to like 120 something. Check that asap.
I havent messed with anything except I moved some case fans around and opened up my case. It hasnt dont the shutdown thing since. I think I just need better cooling in there. :|
I remember that my old graphics card, which I bought was second hand, was incompatible with windowsxp, it would cause the monitor to flicker, and after a week or so, the drivers would change the refresh rate. Try your graphics driver, check it upto date, just to be careful, if you can install it in safemode, also make sure you remove in safe mode. Make sure you let us know how it goes.
are they load or idle temps temps? In either case I would say that 57c is too high... I know that an AMD will operate up to 85c but it won't be happy. I would recommend a new hs/f and maybe some AS5.