Welcome, Newcomer. Please post the components used to build your system. Next please clarify what is going on.
Does the computer turn on, stay on for ~30 sec, then restart and loop?
Does the comptuer turn on, stay on for ~30 sec and then shut down?
Without knowing your system components, it will be hard to help you diagnose, but i'd start with the troubleshooting guide. Just follow the link in my signature. Work through every relevant step in the guide.