lost network and internet connection

I have 2 PCs on a network that are so slow they are not usable. Both are in the same office.
I have norton 360 on all 10 PCs but these 2 have gotten hijackers hotbar, ibis, huntbar

1.I cleaned them with spysweeper, spybot and avg
I now can get a very slow internet connection, but still with problems. Norton will not update.

2. I can only login in safe mode under the local computer, not the network.
I have cleaned it in safe mode with AVG and sptbot, but cant get updates in safe mode. adaware gives me the message that it cant install due to system policies. I am loged in as the admin for local. No admin login works it hangs for a few hours.
any suggestions on how to troubleshoot these?
thanks

Jan