Is this a wired or wireless connection?
If its a wireless connection check your cordless phone. This is from personal experience. My 802g card works on the 600mhz range .. so does my cordless phone. Hence, when the phone was in use all kinds of fun things happened with the wireless connection. And then it was hell getting the connectivity back. It's just an idea.
I still haven't bought a new phone! Funny, I bought a new PC before I'll buy a new phone. That's funny! I prefer to stay hard wired! =) Although it's fun to mess with my neighbors who .. refuse to lock down their wireless network.
But thats a suggestion. If thats your case.