MSN-Windows Messenger

Hello!
I have downloaded the latest(?) version of Windows
Messenger to obtain an update, as the HELP file of the
MSN Messenger informed me, that this was needed to be
able to share applications with others. I did receive
some warnings, that I would loose my connection with
some "Instant Messeging Service" or something similar,
but as a fool I went ahead, anyway. Now I cannot sign in
to Windows Messenger at all, the sign-in table just keeps
coming back, although, the MSN Messenger does not seem to
be effected. What is happening here? Before, I could use
either of the two Messengers, although, not at the same
time. Could anybody help me out here?