Can’t open Safari on iMac
There are a couple of things you can try


Create another user and log in as them. If Safari launches there is something in your old profile causing this problem.
Failing that reboot your Mac holding down the Shift key until you see the gray Apple logo. Your Mac is now booting into safe mode. It will take longer to boot, so go get a drink and come back in 5 minutes. If Safari launches then there is something that has been installed that is causing Safari to not launch.
Download and run the latest Combo Updater for the same version of macOS that you currently have. For the current version of Sierra the combo updater is here.
Download a cleaning app (I use Onyx). Quit out of all running apps and run the app. In Onyx click on the Automation Icon and click execute. This will take a while, go have two drinks. When it is done reboot. If Safari works then there was a damaged cache or other file that Onyx cleaned up.


Those should be a good start on fixing it.