When I switch my p.c on the monitor goes on stand bye after 5 seconds?

Try moving the power cable around(hold it at different angels) and see if it comes on or tries to. If it is then your plug on the monitor is going bad. Also depending on how the monitor is made(some have the power cord pulling down on itself) it could just be coming out of its socket and not actually a socket going bad.

Also some information on what monitor it is would be helpful