CPU powers on, no video out

[msdmatt]

Every time I turn my computer on the fans spin (cpu and gpu) and the lights turn on (power switch) and it makes one beep like it used to do, but no video comes out. I've tried using HDMI and VGA outputs to tv and monitor (from graphics card and directly from mobo) but nothing. I've also tried resetting the BIOS (moving the 2-prong plug around, taking it off completely, taking out the backup battery). Still nada.
All was fine until I plugged in a printer to it last week but now it won't go anywhere.

Here's my build:
Intel DH55TC (LGA 1156)
Intel i5-750 2.66ghz
Corsair 2x2gb DDR3 1333mhz
Silicon power S70 120gb SSD (windows 7 32 bit)
Antec VP-450 watt
MSI GeForce GT 620 2gb GDDR3
(DVD/CD drive)

Anyone have any ideas why it would work fine for weeks (it's a rebuild from leftover parts) but then stop working?

I don't know how to post pictures but I have a few of the connections to make sure I haven't messed anything up when trying to figure out what might be wrong..

 

[Phillip Corcoran]

Try reseating the graphics card in it's slot by removing it then firmly pushing it back in.

Oh, and the mobo-integrated graphics won't work anyway while there's another graphics card present, you have to remove it if you want to use the integrated one (unless your BIOS allows you to specify which of the two video adapters you want to use).