What OS are you running? What steps have you tried so far?
I had a similar problem with my nexus 7 2012 after 5.1.1.
I recovered mine via fastboot and loading the latest 5.1.1 image from google.
One thing I didnt try was a factory reset and set up as new device and install apps individually and test to see if one you were using was an issue.
I would start with the recovery mode and wipe the recovery cache and restart.
If that doesnt help then factory reset and set up as new device and manually load apps individually.
If that doesnt help then use fastboot to flash with 5.1.1 image from google.
Good luck.