When you say you can read Word files, does it say anything along the top like read-only or protected? If so is there an Enable Editing option? If so click it.
Swapping hard drives isn't quite as simple as just physically exchanging them.
It's normal to have to go into the BIOS of the computer and change some of the settings.
The trouble is ... often, the system only "thinks" it's Ok. You could be really brave and uninstall the mouse driver............ reboot, and see if it picks up a generic Microsoft mouse driver.
Other simple possibilities.......
mouse sensitivity settings
optical mouse on dodgy surface
USB problem ......... try alternative ports
Clutching at straws here, I'm afraid. I just hope one of the usual tech suspects may see this and offer much better than I. It's one of those niggles that really need someone to sit in front of it and try a few things.
So do I, Builder - the Word is perhaps the most annoying as I can't write tonight - even then the cursor may bounce (5 times in typing this)....Thanks though!
The Word problem disappeared when the Truro PC guy re-positioned the cursor drive, something that he had missed. ADblock took a minute to fix and Firefox, well that I'll do, just unload and reload - not that I use it much.