The motherboard and power supply of my computer are about 6.5 years
old. I have been having problems with it lately. It has been
locking up and rebooting itself frequently. The most common problem
is lockups with a blank screen. The other problems in decreasing
order of frequency a lockups with a frozen screen, lockups with
slanted horizontal lines on the screen and spontaneous reboots.

These problems occurred more often at higher room temperatures and
when the CPU is used at 100 percent for more than 20 minutes. I
cleaned the dust out of my computer case. My computer stopped
locking up for about 36 hours and then it started locking up again.
I changed the FSB speed from 166 to 133. I still got lockups so I
changed it to 100.

With the FSB at 100 the lockups stopped. A few weeks ago, the
weather got cooler so I increased the FSB back up to 166. This
worked until today. Now my computer is locking up frequently again
and the room temperature is less than 70 degrees F. I decreased the
FSB to 133 and my computer has been running for 3 hours and 43
minutes.

What is more likely to be the problem, the motherboard or the power
supply? Is there any kind of test I could run to figure out what
the problem is? Thank you in advance for all replies.

--
Whenever I hear or think of the song "Great green gobs of greasy
grimey gopher guts" I imagine my cat saying; "That sounds REALLY,
REALLY good. I'll have some of that!"