a21p shuts down

[Brooklyn]

ok this might be a little long so bare with me.
i just got this laptop from a buddy of mine who really knew nothing about computers. anyway, i got this laptop, re-formatted it and re-installed XP pro. here is my problem, it likes to shut down occasionally by itself. and when i mean shuts down , it just Shuts off! now this computers specs according to IBM are pIII 850 mhz 128 MB (SDRAM) win nt.
i noticed in system properties that it is at 693 mhz and i have 256 mb ram (2 128mb)
it ALways shuts down on me if i try to install AOL. any version.about 20 seconds into the install
i ran a memory test. it shuts down at the same part every time.
now i took out one memory stick and tried to install AOL.. click it shut off.
i took that one out and put the other one in .. it shut off again apon installation of aol.
i just ordered new memory for it. but i don't think this is the problem
Windows is fully updated, and i updated it from IBM too.
i don't know if this computer was doing it to my buddy because he rarely used this thing.
i don't know what else to do.. please give me some ideas/input

p.s. i know AOL Sucks , so please don't reply with "just don't install AOL"
it doesn't just shut off when i install aol, it does randomly, i just don't know why.

[Brooklyn]

oh i don;t think its a heat issue either, because i've left the computer on all night and it didn't shut down. plus i think the fans are working.

[Deb Suran]

Read the second "Sticky" in this section.

[Brooklyn]

i did everything but re-set the CPU chip.. i don't trust myself to take apart the laptop like that
and now after pulling out the little battery,and plugging it back in, it says its running 846 MHZ WTF