No Display

Dear Sir
I have a HP workstation ( DC7600 SMALL FORM FACTOR ). Today while i was doing something with it the display became black and only start menu and the calender gadget could see after some time vaguely . but after some time the display became normal for some time and then became black. the OS is windows 7 (64 bit). I thought 64 bit may be the problem.So I changed the OS to windows 7 (32 bit). The system worked nearly one hour and the display disappeared. No VGA signal comes out ( Monitor blinks ) I opened the CPU removed ram and cleaned the slot. No change . but this time when i turned on the PC the green indicator on the PC became red and alarm sound came . again i tried at that time all the fans in the system rotates in a low speed for sometime and the speed of all fan increased high .
What is the problem ? I request the kind hearted people to help me by giving a solution
Thanking you
Shaji