If the problem is still happening try the following:
FIRST AND FOREMOST MAKE SURE YOU DATE AND TIME ARE SET CORRECTLY (IF THE DATE AND TIME A WRONG AIM AND MSN WILL NOT WORK)
1- Open windows Firewall (I am assuming you have windows if you have mac see below) and check the exception allowed make sure AIM, and MSN are checked)
2- If the above doesn't work disable windows firewall and try again (don't worry you will re-enable if doesn't work)
3- if the above didn't work then you can try using a couple of commands in command prompt to refresh internet connection
COMMAND PROMPT HELP
>(signifies next step) [enter]= press enter key
1- Start > Run (in Windows Vista use search bar at bottom of start menu) > type CMD then press enter > type (must be exactly as written) cd/ [enter] > ipconfig/release [enter] (you will lose internet connection) > ipconfig/renew [enter] ( your computer will now obtain and renew your Internet settings)
I really hope this help