You could have easily fixed it yourself for like 20 bucks at least. Or if you wanted to put better speakers in it would be more, but...
If the computer thought there was a pair of headphones in the input socket - Replace the socket internally. There's only minor soldering and wiring involved. In fact there may be a loose wire, but...
If the computer speakers blew - Either re wire it or replace the speakers. You can get really cheap ones at like 10 bucks a piece.
Flash Player Problems - Have you tried re-installing EVERY SINGLE THING? I mean like the browser, the flash player, etc.? Or did you just recently have this problem? If that was the case, then try downgrading your flash player or switching to FireFox, Google Chrome, or Opera.
Windows Media Player - Did you try re-installing your codecs? Or the whole player? Downgrading?
... Wait? Why am I giving you advice, you already sent the computer away...?