As dhn states, make sure you are disconnecting prior to unplugging.
This happened to mine once, and I just did a soft reset and its been fine ever since. To do a soft reset, open the little bottom door and right beside the card slot you will see a very tiny hole. Stick a pin into the hole and hold it in for about 5 seconds. You should then be able to restart your device.
Although HOME should do an auto update, ensure you do indeed have the latest HOME version and application version. The most current application is 7.901.
You can check your applicaton and map version by touching the satallite bar on the screen, the next screen will show you the version, touch that and the screen will show you the map version, etc.
Its a good idea as well to place that info in your signature line, this helps others help you.
If you purchased and registered your device within the last 30 days, you are also eligible for a free map update. On HOME, click on the Latest Map Guarentee. More often than not, it will tell you that you have the latest map, when indeed you do not. If this is the case, a call to TT support and a faxed in copy of your sales reciept will garner you a new map. I believe that currently, the 8.45 is the latest map.
Cheers!