Doesn't sound too good mate - regardless of what tool, ArchiCAD's intelligent cursor should change from a crosshair to a mercedes no matter what tool you are in. Does this happen while you are in other tools (the Door tool for example)?
Either way, you may try saving the problem walls as a module and uploading so we can check it out.
DITW - Hope you have an inner tube and a cooler handy.
Cheers,
Link.