monitor goes black

I have a Dell 8400 with a 17" E172FP flat panel display, Video Card is DVI/VGA/TV-out) Radeon X300 SE

Yesterday my computer and monitor was working fine. After leaving my computer for an hour when I came back the monitor will not come back on. I have shut the computer off and unplugged from electricity and unplugged the monitor from computer. Left if for over an hour and hooked everything back up. When the computer first comes on the monitor comes on for 2 seconds then goes black and the green light that is on where you turn the monitor on blinks.

Any help from any one would be appreciated