I'd run Memtest and see if it runs without any errors:
Memtest86+ - Advanced Memory Diagnostic Tool
It may be that one of your dimms wasn't seated right. Hopefully it isn't a sign of a failing slot. Time will tell. Good you are back to normal as of now. As far as the Hijackthis log, I'm not an expert, so really can't say. You do haven the latest version which is W7 and x64 compatible.