Hi, I have a problem with my surface pros (I have three of them). When they are working everything is fine. But once in a while they stop charging and go into sleep mode even though they're plugged in, when waking them up the tablets aren't charging but if I unplug them from the wall socket and plug them back in then they start to charge again. Has anyone had a similar problem. If anyone has a solution on how to resolve this problem that would be appreciated.