Computer does not recognize the restart butto

Hello,
whenever i try to restart my computer from the start menu it only hangs there and i have
to turn it off with the switch at the back and wait about five or ten minutes before i can restart it
again. i even changed the power supply and it was ok for a while but now it is back to the same
old thing. it was only about a month that it lasted with the new power supply.
thanks
Alan