|Does the monitor show signs of powering on? I know its stupid, but have you made sure the plug is switched on :)|
This is an odd one though. You said you tried different video cards and monitors...odd.
1. Try the monitor on someone elses PC. This will tell you if the monitor is at fault.
2. Try the video card on someone elses PC.
3. If those two things are working fine, then you can narrow it down to your motherboard. Then its going to be down to your BIOS settings. Check that you have the correct VGA settings etc.