I have a Crate BT220 amp with a balanced line out (XLR) on the back. I have an XLR to 1/4" jack cable which then goes to a 1/4 to 1/8 adapter and into my computer's sound card. When I try to record, I only get buzz. Ground lift on teh amp does nothing. No actual signal whatsoever seems to get to teh computer.

However, when I took a line out to the PA at a show, things worked perfectly. So I know its capable of working, am I just doing something wrong?
bad connection between the converters, too many converters or there's a problem actually on the computer. Try to keep conversions to a minimum especially between XLR and 1/4". For some reason, I don't know why, but XLR has a much fuller and clearer sound than a 1/4". Maybe it's getting overloaded.

Try starting there.

Sorry if I didn't help that much.
have you tried the 1/4" pre-amp out? (if it has one). do you get sound if you plug in the bass direct? it sounds like a simple problem. maybe a bad adaptor?
1/4" preamp out--u mean FX loop?

I just bought the XLR to 1/4" adapter the other day, so I hope its not a bad one. It is a balanced XLR out but an unbalanced XLR->1/4 cable, but from what i understand about the workings of balanced connections that shouldnt matter.
It might not be the right impedance.

Try running the line out through a pedal with a buffered bypass (a pedal without true bypass), then run it into your adapter and sound card.
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I'm gonna throw a few points in here, and hope for the best. It's 2am, and I'm goosed...

For one, the XLR is balanced, to cancel out hum. By putting the signal thro' an unbalanced adaptor, near to a PC (noisy bastards at the best of times...), you're creating a problem right there.

Could be iffy adaptors - I've owned my share of those!

Are you trying to record onto MS Sound Recorder? 'Cos it really sucks donkeys. Even if you're using something like Audacity, you could have levels set incorrectly, which could just cause mucho distortion.

Ground lift wouldn't help, 'cos the PC's PSU has a transformer in it, thus physically separating it from the power source, much like a DI box or ground lift box has.

Have you tried playing something low-powered like an MP3 player thro the soundcard socket, to see if you get an output to the speakers?

Sorry to go on a bit , hope it helps.
Im using Audacity, and it seems like it the levels are set correctly.
Theres definitely no signal coming through--its all just buzz. No matter what I play, how loud i play or what level I set for the line out, its always just buzz. The adapters Im using all work--when I run the same 1/4 to 1/8 adapter from my PC's line out to the amps input, it plays the music on my computer. But when I got the opposite direction, it doesnt work.

Could it be that my XLR to 1/4 is unbalanced? It shouldnt be, but could it?