Thank you all for your help.
Hubby bit the bullet and did a full restore from scratch on the server last night and... fingers crossed.... that seems to be working so far. I am actually able to log in to MSN without it crashing round my ears for the first time in ages.
BasIAm - Yeah, we had tried all that. It wasn't just my lappy but also the other wified puter we have here - everything directly wired into the server was functioning just fine, so it clearly had to be something to do with wifi/firewalls or some such. I am so not a techy person, but thanks for the suggestions.