I have had this problem with a co workers computer.
Once we had loaded AC V81 we found he couldn't enter values into the x & y fields.
When i checked the keyboards shortcuts i found there was no keys assigned for x,y,z,r, & a.
As these were greyed out in the keyboard shortcut menu i couldn't assign the keys either (i assume they are greyed out as Graphisoft does not want the individual user changing them).
I fixed it by copy the preference files across from another computer.
Cheers
Stu