Boot Failure

When I boot my system POST continues for 7 secs and then shuts down.I then press the restart button and POST continues and is successful. M y system win xp pro m/b asrock 939nf4g-sata2. w a gray

Is this a new problem? So everything is OK once it starts the second time?

Is the second start off the reset switch? Is this different from the main power button?

If so are you sure that the main button is not sticking which would cause the system to start then turn off.

If you restart from within Windows does the computer restart?