Have you any way to check your DNS-suppliers setup ?
A glitch here is the most probable cause.
If your DNS-supplier = your ISP, call their support.
Are you still receiving mail from the outside? If not, your nic might have called in its chips, but then again, if you can browse the internet from home we're back to square one.
Hope this helps - otherwise just bang your head against the wall for ten or twenty seconds - its such a relief when it stops! - an then ask again in this thread . . for a while it will probably feel just the same way. On the other hand, if you need a specific reply, just supply some more specific info (Server/Gateway or.., behind a router or.. you can probably figure out the rest for yourself).