The XPS writer is the only printer driver that comes pre-installed with Windows. It might actually be part of Office, but I can't say for sure. Since it's the only driver showing up right now, it was chosen by default.

If you printed before, it was because Windows found a printer on your network that isn't available now for some reason. It sounds like you have a network with mixed versions of Windows. I haven't had the best luck with automatic printer discovery in that scenario. Sometimes they show up, and then they don't. I would start by manually installing a driver for the printer. You may need to manually put the network path in.