TC connects to PC (802.11n) DHCP IP assigned but no DNS lookups

Replaced my Linksys with a Time Capsule. Our iMac works fine. Our MBP works fine.
Just recently our room mates PC is not resolving domain names. Her 802.11n USB wireless connection had been working fine. But now when she connects she is assigned an address via DHCP and her DNS is registered as the TC ( as is ours in Mac land). But her PC is unable to resolve any DNS names.

I hard coded the DNS server of our ISP in her windows configuration and this work-around is working for her. But I would like to understand what went awry.

Ideas?

Warren