alt+tab stopped working

I've always used alt+tab to switch between windows. For some reason it doesn't work anymore - nothing happens.
The keys work individually.

How do I fix this? Also, why did it stop working?

Thanks.

It worked for me. Press ALT then one touch tab. you might see the TASKBAR ICONS. for example i have 3 opened, googlechrome windows defender and control panel. If you have windows defender opened note when you press alt+tab it switches you to the SECOND application

Askboy4 said:

It worked for me. Press ALT then one touch tab. you might see the TASKBAR ICONS. for example i have 3 opened, googlechrome windows defender and control panel. If you have windows defender opened note when you press alt+tab it switches you to the SECOND application

I think I was unclear about my problem.

Alt+tab used to work for me -- it worked fine ever since I installed win 10.

Now it just stopped working for some reason, and I don't know how to fix it. The individual alt and tab keys still work fine.