iMac does not recognize my iPad

I can plug my iPad into USB port on Key Board and it will connect to itunes but not charge. ( I know the keypad

does not have enough power to charge)

When I plug my iPad to a USB port on the back of my iMac, the iMac and iPad

go into a bad Loop and a warning message comes up on the iMac that says it does not

recognize the "iPhone" it does not stop until I unplug the iPad. The iPad had a 90% Charge.

it is as if the connection is constantly breaking between the two units.