My Laptop's Sound turns into slow motion sometimes, What happened?

I have a HP laptop and when i first got it the sound and everything was fine, and then one day the sound would turn into like a slow motion not just the sound, but the video too. Like whenever I play music on the internet or watch something on youtube etc. it will play fine for awhile and then turn into slow mo and the sound sounds like its crackling or something and the video itself would be in slow motion too. I would pause and refresh and sometimes minimize the window and it would be back to normal and then randomly start again. The weird thing is whenever I play music on iTunes or watch something on Windows media player it plays normally without any problems, but if i go on the internet it acts up like that...also whenever i play certain games like rollercoaster tycoon it will do the same thing. I've had this problem for about a year now and tried lots of things but it never goes away. Is there something i have to update or what? Please somebody help!