Blank Screen

Our Compaq Presario S1050AN Desktop Computer,2400 AMD Athlon, 2 gis ram, I press the power switch on it firers up load lights on, Fans are going, There is a long beep continues 5seconds on 4 seconds of,The screen is blank, There is power to the screen & it goes, tried on another, I have systematically removed all the hardware down to a bare board with no change to the beep, can anyone add any ideas to this Is it the Board or the Processor, Thanks Noel