If you have an older Apple iMac it will have a spinning hard drive and it is likely running quite poorly.
In this video we demonstrate how to disassemble a Mid-2010 iMac a1310 a1311 and replace the spinning disk with a SATA Solid State Disk. In the followup video HERE, we demonstrate how to install a fresh macOS on the new drive.
This video below shows that we damaged the LCD screen cable and how we repaired / replaced it
And finally this video shows that you can easily convert your old 3.5″ spinning disk into a USB drive. In our case we used an inexpensive Sabrent USB Hard Drive Docking Station kit.