It might not be a hardware problem. Maybe a reinstall of OS X will help. If your iMac is a 2009 model, you should be able to update to OS X 10.11.6 (El Capitan). Updating the operating system is not that difficult or dangerous, as long as you have good backup, preferably Time Machine.Replaced the battery but still no luck. Old battery was still good reading just over 3 vdc. BTW, it was a 2032. Replaced anyways because it was 15 years old. Also blew out all the dust and reseated some cables and boards. Same problem, I need to cycle the power many times before I get the login screen to show. Once I get that I can log in and finish the boot everytime.
Try using the App Store to obtain El Capitan. From the menu, go to App Store. In the search field (upper left) type in “OS X El Capitan.” If a category for El Capitan opens up, click on the title until you get a new window with the GET button. Click on that and it should start downloading the installer into your Applications folder. If it automatically starts and brings up the installer window, QUIT to abort the installation. In Finder, copy the installer file from Applications to another location on the Mac.I couldn't download El Capitan because my browser is outdated but I did find and reinstall my Snow Leopard disk. I don't want to shut it down in case in doesn't work because it can take almost an hour to get it booted. I will update the thread next time I need to boot it up again. BTW, my Mac is a 2007. I only use it for working out because I can go online or run DVD's depending on which program I'm following. Also, the large screen is a nice option.
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