Internet problem when switching users

[Sundan]

We have Panda Anti Virus whatever and just recently let it expire. We reactiviated last night and when it came back up we started having a problem with our internet. We have 4 different users on this computer and whenever you start up the computer and click on someone, they can get to the internet just fine, but then when you switch users, no one can get on the net without restarting the comptuer again. Does anyone know why this might be happening as it is driving me insane.

Thanks in advance...