My hp starts and then shuts its self down after a few seconds

Try disconnecting all the USB and peripheral devices that you have recently attached and restart the machine.

If that doesn't work it's either a virus issue or a cpu overheating issue.

Boot in safe mode and try running an antivitus first. If it detect a virus, remove it.

If that doesn't work. Try to monitor the CPU temperature in the BIOS or by downloading this program
http://www.almico.com/speedfan.php

If you see the temperature over 60-70 that's too high and that would be the reason behind your problem. In this case you will need to fix your cpu fan or buy a new one.