Harddisk with a ?

iMac (Late 2012) computers came with OS X Mountain Lion, not OS X Lion. So, it could be a 2011. To find out for sure, look at the serial number on the bottom of the stand of the iMac. Then, enter it here: Check Your Service and Support Coverage - Apple Support. It will tell you the year.

However, regardless of the exact year, it is too old to be serviced by Apple, unfortunately. So, you have two choices:

• Use an external SSD as the startup disk to run macOS externally from that: How to Setup and Use an External SSD as y… - Apple Community. If you choose this route, since the internal drive has failed, you cannot follow the exact steps outlined in the linked article. If you can let me know the exact year, I'll post modified setup steps.
• Purchase a new Mac: Mac - Apple. The new 24-inch iMac computers are great! If you go this route, it is generally recommended that you purchase 16GB of Memory with the largest SSD that you can afford.

Jack

Follow the steps at > If your Mac starts up to a question mark - Apple Support

What year is your iMac?

Jack

Then you need to do step 5, contact Apple Support or your local Apple Authorized Service Provider and schedule a service appointment.