Screen problems

Possibilities:

(i) there is a mouse button (usually the scroll wheel) that you can press to make the upward and downward movement of the screen correspond to the up and down movement of the mouse. Test this by pressing your scroll wheel down - not rotating it, just pressing. Check your mouse documentation and settings
(ii) faulty mouse (if it's a ball mouse, clean it, if not, it's a new one that's needed) try another mouse.
(iii) faulty keyboard up/down arrows sticking. (try another one)
(iv) sticky keys in Accessibility options enabled (uncheck box)
(v) faulty mouse driver - (remove from Device Manager and re-boot.)