Only half Internet Connection

Hi!
I have a W-Lan Router where several PC`s are connected, some with a cable
and some with W-Lan (DLink 624+). The router is connected to DSL, and
actually everithing works. Everey PC has Internet, but one W-Lan PC has
problems. It has Internet connection, all browsers are working. But there are
nearly no other internet programs working, for example MSN, Skype, Google
Earth,... The other PC`s are working fine in this respect, so it actually
can`t be the internet connection or the router.
I `ve tried everything to get it work again, deinstalling every security and
firewall programm, even opening necessary ports. I even tried to connect via
cable, but there is no difference. I also reinstalled the W-Lan card.
What might be interesting: The MSN troubleshooting tool says: "Gateway seems
to be offline", but as I said the browsers are working.

Thanks for help

Is there nobody who might know about this?