BT Broadband

I have a PC at home that used to be on a network. A couple of months
ago I installed BT Broadband on it and everything seemed to be going
fine. Then on the evening of 15th Aug, I started getting error message
720: The local and remote computers cannot agree upon a PPP control.
The only thing I had done since last being on the net was try to
reconfigure a VPN connection to my work PC (involved changing the
remote IP address), which had also worked previously.
BT's helpdesk proved no help at all, they even sent out an engineer to
check there was nothing wrong with the exchange or my phone line
(there wasn't), so I went to the event viewer and found a massive list
of error messages, but have no idea which ones are relevant. Some of
them are very wordy, so for now I will just give a list of ID numbers.
Let me know if you need the text as well.
64, 9, 5719, 7024, 20159, 4191, 20103, 321, 319, 6006, 5000. They
refer to such topics as synchronizing domain controllers, missing
registry info/DLL files (iprtrmgr.dll is the only one named), no logon
servers available, NDISWANIP adapters failed to initialise, Ipsec
Driver and Oakley failed to start, and a couple of service-specific
errors (2 & 711).
I only mentioned that my PC used to be on a network because all the
message threads in Groups seem to be referring to problems on
networks, and some of the event logs keep referring to a Domain
Controller, which I'd assumed no longer existed as the PC's no longer
part of a network, and maybe this is a contributory factor.
I've tried a few of the suggestions I've found in Groups, but none of
them have worked, so I'm also thinking that maybe it's a problem
specific to BT Broadband users.
Confused? I certainly am...
I'm strictly an amateur in these matters (perhaps you could tell?!),
so if you could put any/all responses in Janet-and-John language, I
would be most grateful, and please let me know if you need any more
info to help diagnose the problem.
Thanks in advance,
Toby