Reseat the monitor cable a few times...test.
Reseat the video card a few times....test.
If you have a can of compressed air blow out the video card slot.
Since I swapped the very low end graphics card in my PC to a Sapphire HD6770 from another PC everytime I power up the PC the screen goes blank for about 1 - 2 seconds anytime between 2 minutes to 15 minutes after I power up. It seems that it only does this once.
My hardware is
500 watt PSU
Gigabyte GA-H87M-HD3 m/b
Intel I 4770 CPU (3.4Ghz) NOT overclocked
16GB 1600 memory
Sapphire HD6770 1GB
The video card is NOT overclocked. It is currently set to run at 775Mhz GPU (max is 800), 1200Mhz memory speed and whenever I look at the temperature it is never more than around 50C.
When the video card was in the other PC (which only has a E6850 3.0Ghz CPU with a 500 watt PSU) I never had this problem.
Any ideas what could be causing the screen to go blank for 1-2 seconds?