Neemo's right. Disconnect both speakers from the computer you are now using and move temporarily to a different computer and plug in both speakers there. If they both work on that 2nd computer, it's a settings problem or something else within the first computer. If the left speaker fails to work on the 2nd computer but the right speaker does, that left speaker is bad. Most likely you'll need to replace the entire set. New speakers are under $20 at most computer chain stores; Best Buy, Fry's, Staples, etc.