Please ensure that the Scroll Lock is turned off on the keyboard (Scroll lock light should be off).
Alternatively, you may try the following steps and check if the issue persists:
Click on Start -> Control Panel -> Ease of Access -> Ease of Access Center -> Make the keyboard easier to use and uncheck all the options. Click on ‘Apply’ -> Ok. Restart the computer and check.
Please reply if you have any questions.
Thanks for your suggestions. Tried them, but the problem persists. My health is failing so I don't use the computer much anymore, and I've just given up on resolving the problem.