If you have widows xp try to disaple the xp´s own firewall if not disapled.
I had a lot of problems after i disapled it in my computer, it allowed me to go internet but sometimes it just stopped downloading and it didnt allow me to contact other computer in lan....and i couln´t sent enything in irc.
All those were fixed when i change it.
Hope it would be your problem too....easy to fix