Sasquatch Jones wrote:

The laptop 5-minute death period occured while using A/C power adapater. This laptop is never used on battery alone -- even during this test, the AC adapter is connected.

Hmm, then it could be lint and dust have accumulated inside the laptop
case. The CPU is thermally protected. If the BIOS sees the CPU's
temperature rise too high, it can either throttle the CPU (reduce its
duty cycles to make it work less but slows the CPU) or shutdown the
computer to protect the CPU (and other components) from burning up. If
you don't feel much heat coming out the exhaust port in the case then
maybe there isn't much air coming out because of blockage by dust.

Dust is a heat insulator plus it will block air flow. Get a can of
compressed air and blow out the dust. Many folks just blow from the
intake port (often on the bottom of the case) to blow the dust out from
off the CPU and rotator fan and out the exhaust port. That might be
okay but a lot of dust will remain inside the case. To thoroughly blow
out the dust means having to take the bottomside of the case off so you
can direct the compressed air everywhere (although blowing off the
topside of the mobo may be a bit tough). When you have the case open,
be sure to blow out the fan. Hold the fan with a finger to keep it from
spinning when you blow the air at it. Rotate the fan manually (don't
let the compressed air spin the fan) to blow off each fin of the fan.
Then make sure to blow out any other accumulation of dust, like on the
CPU or its heatsink. It may require using a cotton swab to rub the dirt
(which can be sticky) off the fan blades plus any dirt sticking to the
fins puts the fan out of balance.

If you don't feel comfortable taking about the case to get inside to
blow off the dust, get a price quote from a local computer shop on how
much it will cost. Be sure to save a full backup saved onto external
media before taking the laptop to a shop. Accidents happen.