How do I fix my recent apps tab?

[AC Question]

I was just charging my phone and I was just on my computer. I noticed the LED light was blinking a yellow color. Then when I was using my phone I taped on the recent apps button (which was to the left of the home key) and it wasn't working. The light wasn't showing up but it still vibrates every time I touch it. Also my notifications aren't popping up and I don't know why. Please help me!