Cannot boot Imac (late 2009)

If you had macOS 10.12.6+ installed, then you can try booting into Internet Recovery Mode using Command + Option + R.

In order to create a bootable macOS 10.13 USB drive you need to access to another Mac compatible with macOS 10.13 and use the instructions in this Apple article:

https://support.apple.com/en-us/HT201372

Using other methods to create the bootable USB drive doesn't always work. Or perhaps the internal hard drive is bad which can sometimes also affect booting from other media.

Macs are very picky about the USB sticks used for booting so try using another brand of USB stick as the quality of USB sticks is extremely poor.

Yes, a little bit. Try the basics first.Start off with a reset of the SMC/PMU. You could do this by shutting down your iMac, disconnecting the power cord and holding down the power button for 30 seconds. Let go of the power button, wait another 30 seconds and plug the power cord back in; wait another 30 seconds then press the power button to restart your iMac. Make sure a wire keyboard is plugged in; Immediately do Number two: hold down Apple/ Clover leaf/command key, Ault/option key , P and R keys held down together. Hold them all down for three restarts or three bongs , Then release all keys. Then hold down the Apple And R keys together on the last restart, hold them down until you see a gray screen and progress bar. Wait until the progress bar has finished before you release them. This means you were able to boot into the recovery partition. From here you should be able to pick reinstall the OS , After you have picked A language. You should also run disk utility which you can find by moving the cursor to the top centre of your screen and clicking: OS X tools should show up and from there you can pickDisk utility. Run disk first aid. This doesn’t rule out the possibility, unfortunate though it is, that your hard drive might’ve failed. Sadly, they can and do fail without much warning. Running disk utility can verify the status of your hard drive. I hope you Already did a backup.

good luck

John B

If I remember correctly, this model is supposed to have it's OS installed with an external disk (or flash drive). I don't know why your installation disk doesn't work. If you can use someone else's Mac I would put the installer on a flash drive to reinstall the original OS. Once that's done, the you may have to go through the process of installing the subsequent upgrades to get to High Sierra, the highest OS your computer will accept. (It is a good, stable OS.) There is one way I have found to bypass this process. It requires that you have the computer directly connected to the internet with an Ethernet cable. It will NOT work with Wi-Fi. Don't ask me why. What you do is restart in the Internet Recovery Mode (hold down Command, Option, R). Then be patient. You may have to wait for several minutes until you finally get a window that will allow you to download and install High Sierra. I have done this myself on the same iMac you have. I hope this works for you. Good luck.