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Try a different USB cable, and a different USB port on the computer. One wire broken in a USB cable can make it useless.
Try plugging the camera to the computer with the camera turned Off. That might change things, or not... but note how it behaves and that may tell me something about what's going on.
How old is the camera? in months or years since you bought it.
Has the camera been dropped or otherwise subjected to mechanical shock(s) in its lifetime?
Has the camera been operated in or subjected to, temperatures below 32 degrees F (freezing point) or above about 100 degrees F ?
Has it ever been subjected to a humidity higher than 85 % or gotten wet ?
Has the camera been operated in a gritty or sandy environment, such as a beach, a seaside, a construction site, or the like?