Next problem :-(

[Ted]

Having solved my previous problems I now find if I leave Ububtu running
for more than a couple of hours the machine completely locks up and
although the screensaver is running ok I cannot get into the box...
I have tried ctrl alt F1 but nothing happens and a ctrl alt del will not 
shut the box down so I have to do a hard reset.....
Anyone else had this problem....And solved it ??

-- 
Regards
  Ted Wager
   Linux user