Try another USB port on the PC. Perhaps the cable loosened, or the port fried. If another port works, next time you turn off the PC, disconnect power, open it up, and see if you can find a loose cable. Alternatively, check that the port works for another device, like your keyboard or mouse before opening the PC. If the port doesn't work for anything, that's good news for the 7D. If the port on the PC works for other devices, next you'll have to check that it's not fried on the 7D. Hopefully the port on your 7D is fine, but you're going to need a second PC to test that.