Try to shut off the computer complety after taking the GPS out and then wait an hour or so then turn on the computer and try again or if your computer needs updating update it first then try to plug it in.
Booting issues can be caused by corrupted firmware & maps during the update process or when the flash drive becomes write protected. More information on booting issues can be found here: SHARCNET USA Out of Warranty GPS Digital Camera Repair Center
this wad due to a bug in a SW release of Nuvi 40 . I think the SW was not erasing old points in internal log and after some thousands of Km it crashes.
The only fix has been to sent it to Garmin for assistance...