System freeze ?

[Ted]

I am using a gigabyte mobo, athlon xp2600 processor and a nvidea 
graphics card...I have 2 hdds with Libranet on one and fedora
on the other...I have tried several distros on this box and all except
Libranet freeze at some time...When the ststem freezes I can move
the mouse pointer but the k/board is totally locked and the kde clock
does not count down and I have to resort to the reset button.
Knotix,Slackware,Ubuntu and SuSE seem to crash within a couple of
hours but Fedora will sometimes last for a day or so....I can replicate
the crash by deleting mail in my inbox too quickly or calling up apps
from the task bar quickly will sometimes cause it to crash..
Memtest seems to rum forever ok and have tried the Mersenne prime test
and that is ok...I have also opened the case and forced fan cooling into 
it but no difference...Any tips welcome...
-- 
Regards
  Ted Wager
   Using Fedora Linux