Today i have find out the reason. Only when i use my batch file for starting 9 instances of MC, the button don’t work. If i start only one instance with a batch command it works, and if i start MC with the Start Menu Icon and if i open a new panel it works also. It have nothing to do with the sleep mode.
No, i closed all instances and restarted the batch file, and now it works all. Can't reproduce it now by myself. When it happen again i'll test Alt+F1 for the left and Alt+F2.
But i can open a new panel when need another drive, it is not really a big problem.