Alt Tab doesn't work in Windows 10

In Windows 7 and before Alt+Tab switched between applications. Now Alt+Tab flashes screen and stays on the app. Have to do Alt+Tab twice to change.

Windows 10 have more to its core than Windows 7 (fullscreen optimization, affinity & priority settings/gamemode, overlay etc) when running applications which can cause issues when alt-tabbing. But It depends on what you want to alt-tab and what screen mode it is set at. Flashing screen usually tells me that the program you want to alt-tab have changed either the resolution, refresh rate or color profile from your desktop, hence it tries to readjust itself. It could also be the graphics driver.