Adobe digital AND Computer is being blocked

Upgraded to Ad 4.5 and do have now the problem that every download of an eBook leads to a complete stop of every action. AD is blocked as well as the computer even a switch-off of the computer is not possible. The only possibility to come to a new start is disconnecting the Computer from electricity..

Same problem occurs when downloading a book to my eBook-Reader.

Bevor upgrading AD I was using an AD-Version 2 without such a problem. What is wrong?????

Any help is appreciated. Thank you

My computer is an APPLE iMAC with MAC OS Sierra 10.12.