All videos and audio lag on laptop

Well the title says it all.

I can listen to a song or watch a movie (either on youtube or something saved on the computer) for one minute, then the computer goes wild. The audio makes weird sounds and the video lags like mad, when I close the program the computer slows down and it can take about 3 minutes for it to actually close.

Also sometimes when I scroll down on the internet it just starts scrolling reallllyy slow.

Someone told me to replace the battery but I have to order one especially, does it have any thing to do with my problem?!

I have a G62 Notebook, three years old, never made any problems till now..

Thanks!!