Mic Noise

[BertM]

I'm attempting to record through my Lexicon Alpha with an SM57 copy but when ever I plug in the mic I get an AWFUL buzz and it doesn't record. If I plug directly into the Alpha via instrument cable it records fine. I bought the XLR cable today so I can't see how it could be broken already. Anyone have any ideas of what could be wrong?

[Hellbastard]

Do you have other mic you can use to check if the 57 might be the problem? If the 57 is not the problem maybe the cable is wired incorrectly.