Mac is freezing. How to find the problem?
Solution 1:
Try using Apple Diagnostics to check for hardware issues: Restart your computer, then hold down the D key while the Mac restarts.
Check Apple knowledge base on this subject - https://support.apple.com/kb/PH21879
If you get an error-code, check this page for how to follow it up: https://support.apple.com/en-us/HT203747