Hey Darla,
Same thing happened here last week: I bought a TT One XL which came with version 705 (if I'm not mistaken); I installed TT Home, updated it to its latest version, then connected my GPS to my computer; TT Home then offered me an upgrade to version 710, which I obviously accepted. Everything seemed to work just fine, then I disconnected (correctly, mind you) the XL and tried to play with it. As you say, it booted into a grey screen with the message "No maps found". As annoying as that sounded, I didn't panic (I'm a computer pro and I encounter similar events on a daily basis). I reconnected it to my computer and the proceded to manually analyze the content of the internal memory. The (new) maps were there OK, the config file was pointing to them - nothing should have impeded a normal boot. At that precise moment I was stumped. I used TT Home to look for patches (although a few moments before it had reported there were no more updates available) and, what do you know? TT reported version 710 as an available upgrade. 'scuse me? but I had just upgraded to 710 - I had also checked the timestamp and the version on the map files and yes, they were newer than those that came with the device. Oh, well... I accepted the upgrade once more, waited, and then my XL restarted just fine.
So, to summarize:
1. Don't panic, even if you didn't make any backups; the maps (and everything else) are there!
2. Try and use TT Home again and apply any updates to your device (BTW: you did upgrade your TT Home to its latest version, didn't you?).
3. Never "just unplug" your GPS! Always use "Disconnect device" first or "Safely remove hardware" (if you're attached to a different computer, where TT Home is not installed).