Q:

Every restart/boot, kernel panic occurs

Every time I restart my iMac (or just boot it up) I see this:

But after I restart again it works fine again.
I'm using MacOSX El Capitan.
I've tried to replace MacOSX with Windows but I decided I wanted MacOSX back again so I did a disk wipe and I reinstalled MacOSX.
Now this happens every restart/bootup.

A:

If you’re seeing repeated kernel panics, try the following things until they go away.
Do a safe boot: 
Restart your Mac and hold down the Shift key until you see the gray Apple logo. Doing so temporarily disables some software that could cause problems and runs some cleanup processes. If the kernel panic doesn’t recur, restart again normally.
Update your firmware: 
Software Update may also tell you about available updates for your Mac. If so, be sure to install them. You can also check for any firmware updates applicable to your Mac model at http://support.apple.com/kb/ht1237.
Check your disk: 
Make sure your startup disk has at least 10GB of free space; if it doesn’t, delete some files to make room. Next, to find and fix any disk errors, run Disk Utility, select your startup disk, and click Repair Disk. The easiest way to do this, if you’re running OS X 10.7 or later, is to restart and then immediately press and hold Command+ R to enter OS X Recovery.
And at last, 
Unfortunately, the easiest way to solve it is to reinstall OS X over your existing system, and if that doesn’t work, erase the disk and reinstall everything from scratch.
A year ago, updating firmware and Safe boot helped me to fix it on macOS. You can give a try. 

