Loss of network connectivity.

My problem looks like this (it happened on two computers: one with WinXP Pro and one with Win98SE)

I use Eudora to download my POP3 mail and Norton Antivirus on Win98SE (McAfee VirusScan 7 Pro on Win XP Pro)

The problem with both computers is the same, I lost the internet connection (through my modem and LAN)

I was downloading an email, but McAfee found a virus and deleted it, then I disconnected from the Internet, the next time I went online, Internet Explorer couldn't connect to anything. The Internet connection itself works, the ping command too, but none of the internet programs (Internet Explorer, Opera, ICQ, and more) can connect to the Internet

I managed to resolve the problem on Win 98SE like this

I deleted from the registry the folowing

HKEY_LOCAL_MACHINE\Enum\Network\MSTC

All of the keys under that one

Then I went to the Network Connections and Win98 told that my Network Connection was not complete (all the protocols were deleted, only the Dial-Up Adapter and Network Adapter were). I installed the TCP/IP protocol and restarted the computer
The internet connection was alive again

Now for WinXP Pro

The registry key for tcpip is

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tcpi

I deleted it, but when I went to my Internet Connection Properties, the TCP/IP Protocol was installed, but the connection didn't work at all
I can't fix it, please help!