Problems playing videos

I recently got my laptop back from the Dell Depot. They reinstalled the OS software. Now when I try to play videos online they will not play in full screen. The screen turns black, and then the explorer freezes up. I was wondering if anyone had an idea of what is causing this.

Also when I go to restart my computer, it does not restart but goes to a black screen and remains on rather than rebooting.

Thanks for your help.