Uninstalling Media Player equals problems

Recently I uninstalled Windows Media Player 8 and
reinstalled version 10. When I was uninstalling
WMP I was warned that removing files may incur
errors...and it has. I can not access MSN messenger
anymore, I get a message saying my password is incorrect
or wrong user name. I have followed trouble shooting
instructions...but no luck. Whatever I have done has
also restricted me from access some sites, such as
windows update, hotmail, my internet banking and my uni
email site. I have limited computer tech knowledge, and
obviously shouldn't have downloaded Media player 8...Is
there a way of fixing this problem? I have Norton (in
case this is effecting things). I really would
appreciate some help on this.