Okay, I'm running Windows XP home, 32 bit, on a Dell Dimension E521. It's using the standard on-board sound card, and drives are up to date as far as I know.
I've been using a Samson C01U microphone (which connects via usb) for a few years now, which has never given me any trouble up until now. Then a few weeks ago it suddenly goes haywire, and I can't even get a fully intelligible sound from it, let alone a usable recording.
It seemed to have no problem with the mic on my old logitech webcam, so I don't think the sound card is the problem.
I eventually decided the mic was shot, and ended up replacing it. I got by over the last couple weeks with my crappy webcam mic, until the replacement C01U arrived... and it yielded the exact same results as my "Broken" one.
I guess something is wrong with my PC, but I haven't a clue what it could be.