Aim talk problem - please help

[matti-kun]

ok I had aim and the talk worked fine and all, but the other day my computer crashed and I had to restore back to factory settings and stuff. i've uninstalled and reinstalled aim, but whenever I try to talk now I get the:

Connection problem with <insert name> no connection was made.
Note: Talk may not connect if you or your buddy is using a proxy server, firewall, or NAT.

what could have happened? what can I do? please help

thanks