My iMac screen sometime times shuts off for a minute on its own

Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click https://discussions.apple.com/docs/DOC-250000211

Unfortunately your computer has a number of issues, first is it's age. It is now 12 + year old and has been considered obsolete for many years now. I mention this as it is entirely possible your hardware is failing. For this reason I recommend that you consider replacing the computer with a more up to date machine.

Next, I see some alarming items:

• Adobe Flash is still installed and is a security risk, Adobe has obsoleted Flash and recommends that it be uninstalled. Please visit Adobe's website for instructions.
• You have a large number of third party apps installed that could be considered cleaning or third party maintenance apps. These are 100% unneccessary and frequently have the exact opposite effects on Mac OS that a user wants. They tend to make Mac OS slow, appear buggy and give unexpected behavior similar to what you are experiencing. My recommendation would be to backup, then reformat which erases everything on the computer and then re-install Mac OS and start over.

Your welcome and good luck.

You have not provided much information so we are guessing a little. Did you set the computer to go to sleep after a minute? If you don't know, check System Preferences - Energy Saver.