ADSL Problem

Recently I've had trouble connecting to programs like MSN Messenger. It usually kicks me out about five times an hour, without me even doing any file transferring or anything. I thought it might have to do with my Norton firewall so I disabled it and installed AVG and Zonealarm. Since then, I haven't been able to even connect to the internet in the mornings. It's disconnected really often. I'm networked on ADSL with a couple of people and theirs is all fine (it's worth mentioning that they didn't have the same problem as I did with MSN)... any ideas on what might be causing it?

Thanks a lot.