Why does the scroll sometimes not work?

I know this question has been posted before, but my problem is slightly different. I have synpatics touchpad with my laptop. Sometimes, the touchpad scrolling does not work, but my actual wireless mouse scrolling works. Sometimes my wireless mouse scrolling does not work, but my touchpad scrolling works. Why does this happen? The problem itself is not consistent. The scrolling usually stops suddenly. Scrolling works perfectly fine for a webpage, but then it stops working during the middle of my scrolling. This problem started to bug me. The problem still exists with Firefox reinstalled and without add-ons.