Help…. I have a blank monitor all of a sudden.

This is my first computer rebuild as of yesterday I had it running and was in the bios and changed it to boot to CD ROM. It was running pretty slow and I called a tech support. The guy wasn’t helpful. All he said is it might be grounding out and to pull out the motherboard and check. I did and put everything back together and now I don’t have video?!!! It has an intigrated video, I’ve checked the RAM, cables, power supply both the the computer and monitor, used different monitors and checked monitors. It is not the monitors it is the computer. Does anyone have any ideas?