I have a gray screen on my iMac upon start up

Do your know the sub-model of the iMac? Your equipment line includes "10.11" which is a very old macOS version. Apple only works on newer models†. It appears the currently the oldest iMacs they still service are the late 2015 models.

IF the computer will not start, look in the bottom of the metal stand's "foot" for the serial number:

Then enter the number into this Apple support page to see if it returns a sub-model description:

Check Your Service and Support Coverage - Apple Support

In this example...

..."(27-inch, Mid 2010)" is the sub-model of that iMac.

With the sub-model, we can better advise you whether to contact Apple support, or find an Apple Authorized Service Provider who still works on older Macs.

† — Apple Reference: Obtaining service for your Apple product after an expired warranty - Apple Support

Have a look at > If your Mac starts up to a blank screen - Apple Support

Also see > If your Mac doesn't start up all the way - Apple Support

Sorry to hear that.

At this point you need to contact Apple Support

Or call and schedule a service appointment at your Apple Service Provider.

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