Many thanks one and all for all the suggestions.
picked up the computer and brought it home to play with and lo and behold it all works, plug in any memory stick anywhere and it responds correctly. ( this often happens to school computers, I put it down to a ride and shake up in the rickity transport!)
and yes I need try the removal all power before doing that! but to no effect whilst at school
However its not a particularly convienient method or quick.
So I'm still on the quest of deleting and then re installing usb drivers in device manager when using a usb keyboard and mouse, but at least have the luxury of time to look about for the answer.
Rick