USB Conflict between wlan and modem.

When I first ste up this machine all worked well till My Wlan provider went
down. When it got fixed I could not get Both my WLAN and Modem (both USB) to
work together. I can run either one of them alone but not together
(alternatly of course).
I have tried all diff ports and both devices say they are on and working
properly. They just won't complete the handshake