iMac 27inch Mid2011 kernel panic

Try recovery mode (Cmd+R on startup). when in recovery: Try to repair the HD in Disk Utility, reinstall OS X (it shouldn't delete anything, just repair itself) If these things don't work, its most likely hardware related.

Cheers,
Adam

I had the same issue, Taking it the the Apple Store will save you frustration, they can preform a hardware test there.

Cheers,

Adam

iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program - Apple Support

Why don't you post the panic report and let us take a look?

These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.

Please launch the Console application in any one of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

In the Console window, select

DIAGNOSTIC AND USAGE INFORMATION ▹ System Diagnostic Reports

(not Diagnostic and Usage Messages) from the log list on the left. If you don't see that list, select

View ▹ Show Log List

from the menu bar.

There is a disclosure triangle to the left of the list item. If the triangle is pointing to the right, click it so that it points down. You'll see a list of reports. A panic report has a name that begins with "Kernel" and ends in ".panic". Select the most recent one. The contents of the report will appear on the right. Use copy and paste to post the entire contents—the text, not a screenshot.

If you don't see any reports listed, but you know there was a panic, you may have chosen Diagnostic and Usage Messages from the log list. Choose DIAGNOSTIC AND USAGE INFORMATION instead.

In the interest of privacy, I suggest that, before posting, you edit out the “Anonymous UUID,” a long string of letters, numbers, and dashes in the header of the report, if it’s present (it may not be.)

Please don’t post other kinds of diagnostic report.

I know the report is long, maybe several hundred lines. Please post all of it anyway.

When you post the report, you might see an error message on the web page: "You have included content in your post that is not permitted," or "The message contains invalid characters." That's a bug in the forum software. Please post the text on Pastebin, then post a link here to the page you created.

If you have an account on Pastebin, please don't select Private from the Paste Exposure menu on the page, because then no one but you will be able to see it.

The page has been removed.

The panic is caused by a kernel bug. Please turn off the firewall in the Security & Privacy preference pane and see whether the panics stop.

I should add that the bug is triggered in many, if not all, cases by "Spotify"—but it's a bug in OS X, not in Spotify. Since you are a couple of versions behind the times, the bug won't be fixed until you upgrade to a newer version of OS X. But the current version still has the bug. You can avoid the whole problem by leaving the firewall off. You almost certainly don't need it.