Posted 15 August 2006 - 02:43 AM
I agree with Ink about the overheating part. The first computer we bought (custom built from a local place) needed to be taken in at least once a month (Needless to say that place went out of buisness fast). One of the fans blew out, and it was overheating. It would just crash or shut down, it was always unstable. It's a typical symptom of overheating.
If every computer you have does that, it may be where you're keeping your computer? Are you keeping it in a closed up area (A desk with a back panel, in a corner?) if that's the case, that might just be your problem. Like any electronic device, even more so, computers need ventilation, otherwise they overheat. Try moving your computer into a more open area where there's more airflow all around it, especially around the back.
Try unplugging the computer and open it up, check to see if there's any dust built up on the fans or anywhere else where airflow is required, get a can of air (Available at most stores, in the computer section) and try to blow some of the dust out. When you're done doing that, plug the computer back in (While the case is still off) and turn it on for a few minutes and check to make sure the fans are working, ESPECIALLY the heatsink fan. If any of the fans appear to be broken or malfunctioning, close up your computer and take it in for a replacement fan.
Now, if you mean just the operating system is unstable, your best bet is to try some virus protection and spyware removal tools to see if there's something eating up your system resources and cluttering up your computer.
I hope this helps!