I was using my usb speakers at work, came home and now, lo and behold no sounds from internal speakers, please tell me I'm just doing something stupid and it is an ID 10 T error. Thanks
System Preferences > Sound, then Output. Verify it's set to internal speakers. If you are talking about alerts, you can set that to "selected sound output device", and they will automatically switch to whichever is selected for output.
Ah I was going to say what he said, try plugging in the speakers and using them and then unplug them maby the system thinks that externals are still plugged in, and try all volume related buttons and switches. Maby restart it lol. I think u can do a hardware check using the re instal disc, but not sure if it checks speakers (I think it should). If all else fails the old fashion way is always helpfull try hitting it lol dont do that.
I know that you stated that they are USB speakers, but sometimes the headphone jack gets stuck. Try plugging in headphones to see if it works. I doubt that this is the problem but worth a try. I assume that you already tried to reboot, and reconfigure your sound. Also check that it is not trying to connect to a bluetooth headset.