WindowXP shutdown problem

My friend has a winxp and recently he has problem shutting down is pc.On selecting the shotdown button nothing seems to happen and he still can do other thing like opening folder etc.....However if he elect to use keyboard ..pressing window and F4 then cycle thru those three button then select shutdown with his k/b it does work at least on few occasions but definitly not with the mouse .Need help and thanks in advance .