No signal to monitor

There is no signal coming from my computer to the monitor. The monitor constantly stays black and the green led keeps flashing although the rest of the computer seems to be working. All the hard drives start spinning and power to the cd rom and dvd rom light come on. I am unable to tell if the computer would be beeping or not becouse I do not have the speaker connected. When I diconnect the monitor from the back of the computer it says no signal. I have onboard video and have tried a pci video card from another computer still with no luck. I have also tried disconnecting everything on the inside of the computer except the cpu becouse the heatsink is hard to get off.

Any help would be much appreciated.