Well, if you could give us some more information we would gladly help you
First: Are you using Windows Messenger or MSN Messenger (Just in case...MSN & Windows Messenger look alot alike)?
2nd. What version of MSN/Windows Messenger are you using? If you don't know, open up the main MSN/Windows Messenger version, click Help, and then About, it'll say "Build x.x (xxxxxxxxxx)" where X is a bunch of numbers. Copy those into here so we know what version of MSN you have.
3rd. Do you get any kind of error message or anything that might give a hint to what is wrong?
And finally...
Can you login to Hotmail without getting errors?