The procedure I use to flash my unit is this:

- turn off the device
- plug the charger in the electric socket
- plug in the cable (both ends)
- run the flasher application on the PC
- plug the charger in the tablet

this way I don't have to press the home button (but it's always better to have it pressed).

I think, however, your problem may be related to the micro USB adaptor.
Is it a Micro B adaptor ?