Q: My iMAC keeps crashing then restarting, getting into loop of restarting

There are many reasons why a Mac might restart itself so try the troubleshooting steps mentioned here > OS X: When your computer spontaneously restarts or displays "Your computer restarted because of a problem."

If you were able to run disk util, then try booting while holding down the shift key.

This will boot the machine in "safe mode" with limited access and 3rd party software disabled.

Let me know what happens!