I recently installed a Garmin Nuvi that I won which works fine, but several days after the GPS installation my XM receiver no longer works. Does anyone know how to fix this - I suspect that the two devices may be interfering with each other.

I've got a Garmin Street Pilot and an XM Roady sitting side by side in my car. They work fine together. I don't think that's your problem.

Mio gps and sirius replay with no problems here

My GPS does not interfere with the XM setup in my truck.

The frequencies of GPS and XM/Sirius are pretty far from each other. But quite possibly something could be wrong with your GPS unit causing it to send out interference on the XM/Sirius band. When you unplug the GPS unit does the XM radio work again? What do you mean by not work? Searching for signal? No audio?