Cant play videos for long.

For a while now my girlfriends laptop wont play videos for a few seconds without freezing. I put freezing as the best way to describe it, but when either of us loads a youtube video it will play for maybe two or three seconds then the video will stop but the sound will continue for a few more seconds til the whole thing is froze.

I looked around and people said they were having problems with add ons.When I looked I noticed Java platform SE was "known to cause security or stability issues", and Java Development Toolkit is "known to be vulnerable. Use with caution".

I disabled both of these, hoping it would help but it did nothing.

Any help would be appreciated.