I have Vista, I use an ethernet connection because I live on the top floor of my apartment and the signal strength is too weak from the wireless here.

Oftentimes, and seemingly without cause, I'll get "limited connectivity" as indicated by a hazard sign over my network icon in the system tray. Now I read all over the tubes during one of the times it was working, and disabled IPv6, and it didn't seem to help.

My connection comes through a modem downstairs, to a switch on the second floor, then a loooong cable to my laptop in my room. Also, I pried off my caps lock and WN keys and my engineer room mate thinks I must have f***ed up my integrated network card (i.e. physically damaged) when I did this.

Sometimes it works, sometimes it doesn't, and it will randomly work or not work without anything happening in between. Of course, intermittent internet is a problem because:
1) I have lots of assignments due online (this is not the future, this is t3h g4y)
2) I often have red lag on BNet and apparently lag sometimes in game even when I have green

When it's working, my connection is pretty fast. So I'm just wondering if it is more likely: a damaged cable, a damaged network card, a connection that is too long, something else.

A cable of this length is pretty expensive, and I guess I could test it with some other random cable, but if it works that wouldn't tell me if it's the length of the cable or the fact that this one has some damage somewhere.