Don,
    I had a Dell computer do the same thing a few years back.  I
turned it over to a Dell tech at the University where I worked and he
fiddled with it for 3 days.  After a while, he got ticked off and
played the hunch of replacing the motherboard and all was well.  I
don't know if the motherboard issue is the same for your situation.
If you have the ability to boot off CD on the Acer Aspire, I would run
Memtest 86+ to see if the ram memory might be a factor here.  I want
to say it won't, but then again ram is cheaper to replace than some
motherboards.

http://www.memtest.org/

just my two cents,
Derek Buchanan

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