First, I have an old issue which may or may not be related:.
Issue 1 (This is an old issue that I have chosen to ignore because it is rare enough to do so) Sometimes my computer turns off by itself. I have rejected thermal-related problems because one of the days it ran 12 hours without incident was VERY hot. The fan ran all day, but no shut down. Sometimes it will shut down 10 times day. Then it will be fine for a day or two.... seemingly independent of temperature. One clue: It NEVER restarts after one press of the on switch when it crashed in this way. It ALWAYS takes two presses.
Issue 2: (as of today) The computer (a five year old Dell 360 Workstation with 1G Ram and 7 Gigs (?) of empty HD will boot without problem and then start to run extremely slowly after 15 minutes or so. The reason for the guess regarding empty HD space is because the system is SO slow I gave up asking it. I checked this morning and remember about 7Gig free. Using Process Explorer, I cannot see any program hogging resources. Idle remains very high. Control Alt delete will open its window, but it too is VERY slow to open. Opening or closing a program can take many minutes. Everything was fine yesterday (a day when the room was unusually warm.)