Downloaded speedfan and im getting the "flame" graphic for cpu and 80C..
I suggest downloading "Core Temp" to be sure of your temps as Speedfan is not always accurate. If it really is 80C then it's running pretty hot which might cause the problem but it could be many things. I'd also run memtest86+ from a floppy, CD or flash drive to check the RAM.
If you need to re-seat the HSF, use only a very tiny amount of TIM about the size of a grain of rice or less.