Well. Tried a new mouse. That cured the problem for a few hours then started again. Tried deleting and reinstalling IE 5.0, sounds like 5.5 might be just as bad.
My keyboard and mouse have different leads so can only go into specfic sockets, but I have checked this and tried the mouse with an adapter in another socket. Same probs. Also looked for conflicts but none found. Did a scan disk and quite a few problems came up, again, cured it for a while but its back!
Driving me mad! Works for varying amounts of time.
Could be something overheating, my fan/ computer have been making some odd noises, like surging fan or something.
Any other ideas?