possible faulty ram slot...try swapping the ram from it's current slot, into the other slot.
possible faulty ram stick....
possible faulty CD drive...
possible faulty CD media...
possible failing CPU TIM... disconnect fan and run system in the bios screen monitoring the temperature for a few minutes and see if the heatsink gets hot as the CPU temps go up. if not, the TIM is toast and not pulling heat out of the CPU...replace thermal CPU paste. scrape that yellow crap off and replace it with some good stuff.