Why is my Notifications bar recent button and home button not working ?

[AC Question]

I have bought a one plus 3T this April , and was happy with it . But I started having some problems with this device recently , I was texting my friend when the battery died and the next day when I turned it on the notification bar cannot be pulled down the home and recent buttons are not working , I tried rebooting my phone but it's of no use and more over I cannot change from user to guest mode
Please do give your suggestions as soon as possible as it would be helpful