No video input on dual monitors

HI chaps n chapesses.
I have a gateway DX4300
AMD Phenom II x4 805
built in ATI 3200
Extra ATI 4350 with dual monitors attached
8 Gig ram, 1TB HD
phillips 244e and a samsung syncmaster 940bw monitors
I dont game but I use many many programs at once, and after about an hour my screen goes blank. then I get a "no video input"
My computer has stopped working but is still on and has to be reset by unplugging otherwise it wont come back with vid working.
Ive had the computer for about a year and never had problems apart from lousy speed until about three weeks ago.
I looked at my windows update list and it says that ATI updated but I cant seem to roll it back.
Help please?
 
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