My PC has suddenly stopped starting up. On checking with case open, the CPU fan starts running when the power is turned on, but it stops after about 2-3 seconds, restarts again after about 2-3 seconds and the loop is repeated. There is no beep and nothing appears on the screen. On searching the internet, I found there could be several reasons for this. I tried removing hard-disk, CD drive, tightening connections etc but of no avial. I also tried using a new power supply but the response is the same.

Where could be the problem and how can it be solved? Thanks in advance.