My Aspire 5750G laptop is misbehaving - cursor racing ahead as if holding down the space key

My Aspire 5750G laptop is misbehaving today - intermittently. In Word documents, Outlook emails, searching on Google etc, cursor keeps racing ahead as if I'm holding down the space bar. When I backspace it just races forward again. When I position the cursor with the mouse and click, it pauses but the minute I start to type it races forward again. If I go back in the text and start to edit, it races forward and erases what I've already written. I've rebooted the laptop a couple of times, have disconnected and reconnected the mouse, have tried running the computer troubleshooting diagnostics.  Any advice for what I can try? It's still under warranty so I suppose I'll have to go through that palaver, but if anybody else has had this problem and learned of a fix, I'd really appreciate it.

Thanks!