AHH! Why is my computer not starting up?

Ok, don’t laugh at my string of technology-related questions….

So, now I got a usb wireless adapter, installed it, got the internet running, and was all excited I so started some software updates (since my computer hasn’t been connected to the internet in months), I logged on Skype, plugged my webcam in, and when I clicked to call someone… my computer completely froze. Couldn’t force quit or anything. Finally I just held down the power button to shut it off and then restarted it. It only got up to ‘Starting Windows Login’, and stayed there for a long time. I tried a couple more times (shutting off, leaving a few minutes, turning on). Then I tried unplugging the wireless adapter and the webcam. Still didn’t get past that screen. I tried taking the battery out. Finally one time I put the wireless back in, and when I do that it goes past that point to ‘Starting network file system’. But it stays there (for at least 1/2 hour). I tried escape, apple-alt-escape (not having any idea if that’d be helpful)—- I can move the mouse freely but that’s it and I have no ideas. I just went through mac website support pages but I’m not finding anything I haven’t tried.

WHAT DO I DO????

[p.s. for anyone following from previous questions, I had cleared 2gigs of space before this happened, if that makes any difference]