Installed basic new system files and now we cannot shut down or restart (only by turning power off then on). Sometimes the screen freezes, sometimes get a bomb message, either 'Finder error, unimplemented trap' or 'finder, error 10'. We have not installed any RAM recently, the fault still occurs when we start with extensions etc. off. We did have a diskdoubling programme installed but this was removed when we installed System 7.6. We also took off Norton Utilities and SAM. The Mac starts OK and the programs run OK. We just can't turn it off! any ideas?