Wow! Been there this past month and bought a whole new system including a case. My old board wasn't all that old, A8N Asus SLI, but kept having freezes and my system would reboot while burning dvd's. Did everything--swapping out video board, Power Supply for a larger one, RAM, and so on.
No ideas, just giving you the benefit of my recent terror. Forunately I've been keeping images of c:\ and backing up all my important data on a regular basis. The data is worth more than the guts of the pc!
Good luck