Soft key are not functioning & notifications are not shown anymore

2 days ago I was encountered with a problem on my Nexus 5 which is about two of my soft keys miss functioning (Home and Recent keys) and also the notifications which are not shown anymore.

It occurred after my phone turened off because of a low battery and when I charged it and turned it on, this happened.

So I searched a lot but no specific solution was found. I waited for an answer from the google support and they didn't give me a feedback.

So I just installed the latest update of Android 6 for nexus 5, but the problem still remains.

Please let me know if there is a solution.

Thanks