[apumic]

Has the 57 ever worked properly?
You might bring it to a music story and ask them to check its authenticity. There have been quite a few sellers selling counterfeit 57s and 58s (as well as some other popular name brand mics.... Neumanns are another popular counterfeit, for example -- at the other end of the spectrum). Another way of telling it might be a counterfeit is to look for any chinese or strange lettering, words, or symbols on the mic itself, but your best bet is to have an expert take a look at it.
In the future, since you can get a new 57 from a reputable dealer for $99, it might be best to go that route so you know it's a good mic!

Anyway, back to the rest of the question. Do you have any other mics you could check the rest of your signal chain with? If you haven't tested the rest of your signal chain, it's possible the problem lies elsewhere -- a bad XLR cable (or one crossing an electrical line in your home), a pre-amp going out, a bad ADC (Audio to Digital Converter), etc. When it comes to trouble-shooting, you really need to isolate where the problem is coming from before you can solve it.