Sound preference issues with Snow Leopard

hello!
have late 2009 13" macbook pro -
i've been late in updating leopard snow leopard, though latter came out month after bought laptop, weekend, did.
mac has 'red light' problem in headphone jack , i've been unable fix it, use external usb speakers. however, i've updated snow leopard, sound preferences refuse keep usb speakers output sound. i'll open system preferences, select speakers, in few seconds, automatically switches internal speakers output. doesn't stay.

i've been searching through forums help, , came across instruction delete 2 files in audio folder, hasn't fixed it.

ideas?

if need further clarification, ask.

 

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