Possible your AutoCAD is set to use the shift key to add new items to a selection set.
Start a command (say MOVE).
Select the first object.
Press and hold SHIFT and select the next object(s).
Relase the SHIFT key and press ENTER to terminate the selection.
Continue the command as usualy.
If it works you may try to reset the normal settings:
Go to TOOLS > OPTIONS and select the SELECTION pannel. Remove the checkmark near the USE SHIFT TO ADD TO SELECTION