If the controller on your IOE enclosure is displaying question marks "?" for the voltage and current values, there is a communication issue between the controller and the I/O boards.

First, confirm that the fuse located in the rear of the drawer is not blown, if it is the fuse needs to be replaced.  A blown fuse prevents power from being supplied to the I/O boards for measuring the various current and voltage values.

If the fuse is still good, there is likely a short on the communication bus for the IOE enclosure.  You will need to check all of the Cat5 cables for damage or loose connections.