Mac Monitor Black Screen

Yesterday I was playing with my screen resolution and I changed it once - then changed it back... then the screen started kind of 'pulsing'.. so I repeated the change resolution and then back... and the Screen went black. When I restart, the monitor comes on and shows the Apple logo in the middle... then as it continues to start up it goes black and thats it... Any help or advice would be much appreciated. Thanks...

Ok what is this a macbook (pro)/ibook/powerbook a mac mini an imac or a mac pro/powermac?? Does anything happen after it goes black?

I have an older G4 dual 450 tower and a Apple 17" LCD monitor... the older style with the acrylic casing...

After the initial startup with Apple logo displaying... the screen goes blue for a few seconds (as normal) then goes black like its turned off and thats the way it stays from then on.

can you try a differnt moniter?