Last night I shut down my computer properly, there was no power fluctuation/failure (there were no problem shutting down). And the next morning when I try to start my computer, it does not start. The SMPS fan and CPU fan are working fine. I have tested my CPU and RAM too on a friend's computer and it works fine. Even the led near the RAM slot is glowing. My PC configuration is as :
Processor -intel p-iii 850mhz
RAM : 128mb ram
Please kindly give me a solution to this question

If it's not the CPU or RAM, my next two guesses would be the Motherboard or the Video Card. First, if you have an onboard video cconnection and a video card, I would try both of them. Maybe a setting got changed in the bios and it's using the wrong one. Then, I would try clearing the CMOS on the motherboard (eith by the jumper, or take the battery out for a while and then put it back in). Then, try both video ports again.

Before I can begin to troubleshoot your problem I need some more information.

Can you be more specific when you say that "it does not start"?

When you press the power button what happens? Does anything happen at all? Does the computer power up? If so, how far into the boot process does it get? Or does the screen stay blank? Does it produce a POST beep (one short beep being the "All is fine" signal).

There are a few dozen things I can think of causing this problem, so let's try to narrow it down and go from there =)