Spontaneous rebooting may be linked to the 100% CPU usage.

I recently discovered why Guild Wars was rebooting my computer. While playing, my CPU temperature rose to over 60 degrees celcius causing the computer to shut down.
Now, it has never done this in any other game, and directly after rebooting, it started to cool itself back down again to a normal temperature.

I think it has something to do with the fact that Guild Wars uses 100% of my computer's CPU time.
I have never seen any other application do this (Even the system idle process only takes 98-99%), and I think it may be taxing my CPU (And a lot of other people's CPUs) too hard.

your idle processes take 98 % maybe you need to weed out some of those

my cpu at 100% is only running 43C
you might want to be sure yout heatsink is still mounted correctly and the dust bunnies are not clogging things up

No, I mean't system idle process, lol.
It's the process that runs when you're not doing anything.