I am running a P4 comp with 512 RAM and 80 GB Hard disk, I have an external Seagate USB hard disk of 500 GB connected. From past several days the CPU shuts down abruptly but the green light in the mobod as well as the keyboard numlock light continues to glow, further only the red light in front of the CPU cabinet continues to glow. The comp cannot be restarted unless n until the power supply plug is removed n re inserted into the socket. Earlier this was occurring only once in a day but frm past 2 days CPU shuts down 4 to 5 times in a span of 4 hrs. I have cleaned my hard drive from all viruses n malwares . One thing I have noticed is that before the CPU stops the SMPS as well as the Cooling fan of the processor chip run at very high speeds making a noise similar to wind storms. Please help me on this ASAP. Thank you

This sounds like a heat issue. Heat will shut down a system fast. Have you tested the temps for your system? Is there dust build-up? Are all fans functioning?

I hav checked the temperatures through everest software and its 50-52 C, i hav cleaned the cabinet recently using a blower , both the fans work normal, but only when the system is about to crash they run at very high speeds.

50-52c = 122-126F. If that is your normal system temps something is high here. Are you doing anything in particular when the fans rev up before crashing?

What is the make of your power supply and how much wattage does it promise to supply? Can you get your hands on a digital multimeter?

actually i am using the comp without an UPS, might that be causing this