Yes, sounds like it could be the hard drive, controller, or even the fan; if things aren't cool enough they'll shut down. I'd find somebody local to you who has testing equipment and can figure out just what the problem is and fix it and/or get a new machine since you say yours is so old. Did you take it apart at all, look and see if there was anything obvious (burnt smell, etc.)? Sometimes it can just be "gunk"/dust or bugs (real ones :-) or something like engine buildup/sludge in a car making things grind to a halt.