Pc won't "restart"

when i click the restart option. Screen turns black, but the pc stays on. so i have to click on the restart button on the pc unit, which i prefer not to. 

Go to control panel, and check power settings. See what the power buttons do. If everything seems to be ok, so its not set to sleep or something, you propably have some errors in your operaiting system, propably some windows update has failed and caused it. 

So you want to fix your registrys and while you are at it, run the update again.

Ah yes, also

Does the power button do the same thing, or does it actually shut the computer down?