Power Problem I have intel 865 board and 3 Giga P4 processor. My problem is that sometines when i press power button to on the computer it started but with in a moment computer turns off. if i press the power button again now then nothing happen as there is no power (power is still there on board). then i pull out the power cable from back and plug it again then computer start normally. sometines the problem is repeated few times but i repeat the same process untill the computer starts

Hmm, it souds like some of the power cables are poorly fitted.
I suggest you to open the pc and unplug the power cables one by one and the plug them in again, you can even unplug and replug all the cables in your pc.
DONT forget to unplug the powercable to the PSU fist! And dont connect that one until you finnish all the your other work.

Good luck to you

This is an issue with the power management and sleep setting of your machine. Basically when you press the power button and the machine is in sleep mode the machine will resume and then shutdown. Then if you press the power button again it won't work until you hard reset the machine by pressing and holding the power button for at least 10 seconds.

Follow this link for info on setting an s3 sleep state in xp.
Also check your settings by going over the information on this page.

For Vista the S3 sleep state is on by default and you might want to change this. To do this follow these instructions.