Ok this is a tough one so expect a challenge!!

Ok this network was in perfect working order for about a month until about a week ago.
We have 3 computers in this network (all running Windows XP SP2), 2 of them (DAVE and PAT) are supposed to connect to the internet through the 3rd computer(DAD).
A week ago it seems that the connection of DAD to the rest of the LAN has stopped because PAT and DAVE now can't file share or access the internet through DAD.
The turning point in this configuration appears to be when the latest McAfee security suite was installed on DAD.

I've tried;
-Using the network setup wizard on each computer allowing internet sharing and file/printer sharing. couldn't get a connection (limited or no connectivity)
-Then manualy configured IP addresses for each computer in the network. This achieved connectivity between the computers but no file/internet sharing
-can ping each computer (IP and computer names) in network from each computer with 0% lost packets
-When the NET VIEW command is used with computer names or IP's, "System error 5 has occured. Access is denied." from all computers to all computers
-tried disabling McAfee firewall on DAD, same errors.
-tried to disable Windows Firewall on DAD receive error "Windows firewall settings cannot be displayed because the associated service is not running. do you want to start the Windows Firewall/Internet connection Sharing (ICS) service?" i click ok and then get "Starting WF/ICS..." then "Windows cannot start the WF/ICS service."
-I've tried doing a few things suggested in other forums on the net but none of them have helped so far.

I think thats it, i'm trying a virus scan of DAD now but thats all i've got, i have no idea!!

Please help me!! i'm so desperate, this no internet is crippling!

Pat

Thanks very much

Also sorry forgot this bit
i've also tried:
-can see workgroup in network map, and all computers but when another computer is clicked on to explore recieve error "[i]name[/i] is not accessible. You may not have permission to use this network resource...blahblah"
-restarting each computer in safe mode with networking enabled (to get admin rights), no change.

Thanks very much