Did your computer ship with a copy of the installer of original system?
If you have an original install-restore System media DVD, that may help.
{Only one iMac (21.5-inch, Late 2011) shipped with Lion 10.7. Later
than that, the iMac models shipped with Mountain Lion 10.8. Prior to
the Late 2011, they all shipped with Snow Leopard 10.6.x. Later, of
course, by Late 2013, the iMac began shipping with Mavericks 10.9.}
So even though the computer may have shipped with an optical drive, at
some point there were no install-restore DVDs included, but it may have
been possible to make a boot-able system install disc, or USB flash, from
which to reinstall a system when a App Store download may not be possible.
Some that shipped with Snow Leopard on DVD or another OS X version, prior
to the advent of 'no-install/restore discs included' models, can be started up
from a DVD or in some rarer cases, a few shipped with Lion 10.7 on USB flash.
If you had a clone of the working system on an externally enclosed hard drive
it could be used to start the computer + its Utilities may be used to try & fix it.
How much installed RAM was in the computer? How about the hard disk drive?
It may have been doggy because it may have been failing. Too bad the etrecheck
report or some other information hadn't been saved & posted first to this thread.
Oh, the printed advice from Apple, to 'update and OS X' to help with some aspects
of kernel panic, is only partly true. Do not confuse an Update with Upgrade. First, is
a slight change, such as a step in Snow Leopard from 10.6.3, to SL 10.6.8.
Given your computer had been running OS X Lion 10.7.5, that indicates that it
may have been one of the last ones to ship with Snow Leopard 10.6 on DVD.
Unless it was one of a few with Lion on USB flash or special grey DVD.
Without more information on the machine specification and build year data, it is
more difficult to match up the real with other possibilities from the databases online.
If you have a media install-restore DVD, even if not Lion, that shipped with the iMac
it can be used to try & start the computer and get it away from the Yosemite damage.
{If the computer is not ideal for use with Yosemite, the Mountain Lion 10.8.5 system
may have been a better bet; but only when the computer is running well, and be
sure to always have at least two different kinds of backups. One, a full working clone.}
However there may be a problem with the hard disk drive. A genius bar appointment
or a visit to a Apple specialist, may be your best bet if you have no disc utility access
and if the computer may have a hardware problem behind these Kernel Panics.
Did you try these •OS X: About kernel panics - Apple Support suggested methods?
Troubleshooting kernel panics can be a long & tedious path. It may have been due
to some software combination or other source, not necessarily hardware...
•Technical Note TN2063: Understanding & Debugging Kernel Panics:
https://developer.apple.com/library/mac/technotes/tn2063/_index.html
At this point, it would seem as though this angle of attack is no longer open when you
cannot get past the basic startup to see what else is going on. Did you try SafeBoot?
If you don't have an original install-restore DVD for a system older than Lion 10.7.
Troubleshooting gets incredibly more difficult with a logjam on top of an earlier issue.
In any event...
Good luck in this matter.😐
