My computer is driving me crazy! Help! please!?

My computer is stupid because when I use the Window Media Player to play music, it plays fine. No prob. But when i it comes to pther sounds, like a video from youtube.com or sounds fron an online game, noting can be heard. Pls note that the Window Media Player is working fine. The problem is when i try to play sounds without the Media Player like online videos or game sounds like in newgrounds, all i get is complete silence. Ples help!