Computer comes on and right back off

Please can you confirm the Make Model and OS, along with any configuration details like touch screen, backlit keyboard, SFF or tower etc etc.

I've noticed that this can be an issue with Optiplex Desktops. 

• How frequent does this happen? - and does it stop after a certain period?

• How long does the system stay on for?

• Do you see an output on the monitor? 

I believe it is a faulty component in the Power Supply or Motherboard.