Help! 2010 imac 27" - Display doesn't work after long sleep

Hi Punisher8522,

Welcome to the Support Communities! The resource below offers some troubleshooting steps to try when your computer won't wake from sleep.

OS X: When your Mac doesn't sleep or wake - Apple Support
http://support.apple.com/en-us/TS5357

Your computer cannot wake from sleep

Make sure your computer isn't powered off by pressing the power key for one second.

If you're using an external display, make sure your display is not powered off or unplugged.

If you are using a Mac desktop:

• Make sure the AC power cord is connected securely to the computer and outlet.
• Make sure the AC power outlet it is connected to is working properly.
• If your computer is plugged into a power strip, make sure the power strip is not turned off. Check to make sure other items connected to the power strip are receiving power.

Your computer is slow to wake from sleep

If you see a progress bar when you wake your computer from sleep, this is normal. The computer is waking from safe sleep.

OS X Recovery and sleep

The system software your computer uses when started from OS X Recovery allows display sleep. Your computer does not go to sleep on idle while started from Recovery unless you are using a Mac notebook that is not connected to AC power.

Additional troubleshooting

If the steps above do not resolve your sleep-related issue, try these additional recommendations.

Reset SMC

The System Management Controller (SMC) is involved in managing power on your computer. Reset the SMC on your Mac if you are having difficulty sleeping or waking your computer.

Reset NVRAM/PRAM

Nonvolatile RAM (NVRAM)/Parameter RAM (PRAM) stores some power-related settings.Try resetting NVRAM/PRAM if you are having difficulty sleeping or waking your computer.

Test with external devices disconnected

Some external devices can prevent your computer from sleeping. Try disconnecting items other than your Apple keyboard or mouse from the built-in USB, Thunderbolt and Firewire ports on your Mac. If this resolves the issue, try reconnecting your external devices one at a time until you find the device preventing sleep or wake. Check the documentation that came with the device, or contact the device manufacturer for more information.

Try Safe Mode

Check to see if the issue still occurs when the computer is started in Safe Mode. If this resolves the issue, it could be related to a third party software item such as:

• a login item
• a startup item
• a third party kernel extension

Try another user account

Try creating another user account, or log in as guest. See if your computer sleeps and wakes properly from the additional user account. If it does, your issue may be related to one of the following:

• a login item
• an app open in the original user account

You can disable login items from the Accounts pane of System Preferences. Try opening only one app at a time in the original user account to determine which app is preventing sleep. If you isolate the issue to a particular app or login item, check its documentation, or contact the developer of that software for more information.

Last Modified: Sep 19, 2014

I hope this information helps ....

- Judy