PC powers up, No beep, No display

Hello been readin Toms hardware for years, but now i have a problem

Machine has been built for over 6 months, but recently while machine was just sitting, and not in use. Mouse, heyboard, speakers were all Unplugged, and the Monitor cable to video card was pulled unplugged by an angry girlfreind

note:when building machine video card was seated fine, and worked but LAZILY, and i know this is bad, i didnt screw it in, i just left it in the pci e slot and connected to monitor.

now when all the cables were unplugged, i plugged back in, and i received "no source, check connection" on moinitor. so i reboot, and same problem. I open case, check cables some were lose, i seated them back in, same problem. tried two different video cards in EACH of my 2 PCI-e slots, and i still cant get a beep or display

all my fans spins, and lights work. im thinking video card and processor still works, definitely leaning toward some cables not being secure, but seeking advice

amd athlon x2 5200
4gig corshair ddr2 pc6800
1x sata HDD
1x sata dvd-rw
600w power supply
8800 gts

I had a similar issue the other night. I had left the system off for about a week went to power it on and it would power up but there would be no output to the monitor at all. I ended up having to remove a lot of components just to check over the system board and power connections only to find that everything appeared to be normal. I ended up removing two out of the four sticks of ram. The system is booting and working fine now but I am not so sure its a ram issue yet as it could be a faulty motherboard. I will need to do more testing.

Intel quadcore Q6600
EVGA 132-CK-NF78-A1 NF780I SLI R
4GB Corsair ddr2 pc6400
8800 bfg gts
600w antec power supply