iMac 27" late 2012 Help

Your computer is suffering from Kernel Panics which can be caused by either hardware or software which makes them difficult to track down. Common hardware issues are RAM which can be incorrect RAM, unseated RAM or failed RAM, other hardware issues is a failing HD or other components within the computer. Software causes can be caused from anything to running software you should not (third party antivirus, cleaning apps, torrents, etc..) or outdated software.

What would help us is if we had a report on your system to look for obvious issues so please do the following.

The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community

Your system is a bit of a mess. There is no evidence that you ever back it up, if that guess is correct that is a guarantee that you will lose data. It is not a matter of if, if it a simple matter of when. At the very very least you should be using Time Machine to backup ( Back up your Mac with Time Machine ) and you will need an External Hard Disk (I'd recommend a OWC Mercury Elite Pro ) .

You are also operating the computer with Apple's security turned off which is shortsighted and again a guarantee of inviting a mess. You need to restart the computer in the Recovery Partition (hold down Command + R on startup) and install Mac OS. This will fill in missing or damaged portions of Mac OS and will not affect your data. HOWEVER do not do this until you have a full backup of your system to guarantee your data.

Those are the 2 things I see off the bat that need to be fixed.