Running Lucid. Computer worked fine last night, went to bed and found the following problem this morning: (so no hard or software changes)

Computer boots up, screen displays normally; date & time correct, background normal, toolbars OK, everything looks normal. Cursor moves round screen in the traditional manner but clicking produces nothing, not left, right or centre. Nothing will open.

Tried restarting, using different USB ports and a different mouse. Have reduced system to minimum; monitor keyboard mouse only.

Does anyone have a suggestion? Thanks in advance, David D