"No Signal" error message.

Apparently my 2 year old computer has a problem I have been unable to solve. I have added nothing to the computer. I hear the computer start up, hard drive sounds like it starts, fans come on, but am not getting a signal to my monitor. I checked my monitor, keyboard and mouse and the wiringon another older computer , all seem to work fine.

Also tried the unplug , hold down the start button on the computer for a minute (even 2) a couple of times. No help. Tried the F8 key, still nothing but a black screen. Only shows the "no signal" messare for 10 seconds then NOTHING Else. Please help.

Jim