Monitor picture is flashing on and off. Please help

[b lurkn]

Here are my systems specs.
Intel I-5 3330
Intel boxdz77ga70k
600w thermaltake psu
12 gb ripjaw ram 2x4 and 2x2
Windows 7 ultimate
OCZ 128gb ssd
750gb hdd
GTX 460


my screen now flashes on and off, on and off but i can hear sound. and teh monitor isnt losing power just signal temporarily
this happens once evry 20-30 seconds
SO i figure my old card did now go out so i replace my gtx460 with a radeon hd 7770.
well i plug it in and the same thing is happening so obviously its not my cards.
so what do i do now.

 

[b lurkn]

and i just tested all my ram so that doesnt seem to be it either

EDIT: i switched my dvi cable to a vga (using dvi to vga adapter) and its happening less but still happens here and there