Q: After startup my iMac's screen turns black

Will it start more normally if you choose to hold the Shift key down through startup and then you may be able to see the desktop and login...? This would be SafeBoot mode.

If so, then it could be troubleshooted or console utility logs looked into, to see if there is any evidence of system parts not loading properly, or of a hardware issue. Or a graphics problem after the system loads.

SafeBoot starts the computer in a reduced OS X so several items are turned off.

With an AppleCare plan in effect, you should consider making an appointment

with a Genius at the Apple Store, to take the computer in for diagnosis.

Especially if this repeats itself; that would make it easier to prove a point.

Have you used this computer with an external display?

In safeboot mode, if it starts you could check some other things in the system.

However there are keyboard shortcuts on startup that

may be able to troubleshoot past the problem.

•Intel-based Macs: Resetting the System Management Controller (SMC)

http://support.apple.com/kb/HT3964

•About reset the NVRAM (so you tried it, more than twice?)

http://support.apple.com/kb/HT1379

PS: there may be two things to try:

two workarounds:

Put the computer to sleep (close the lid on a Mac Book (pro) or press the power button quickly on a desktop Mac. After a few seconds of sleeping, wake the computer up again. The login dialog usually appears now.

2. Sometimes you do not want to put the computer to sleep because you do not want to interrupt a task that is running. In this case, press CTRL+SHIFT+EJECT. This keyboard shortcut usually locks the screen. In out case, locking the screen also enables or resets the screen saver, so that the next key press or mouse motion will bring up the login dialog.

Good luck & happy computing!

I found my computer in the same position today.    Turning it off and restarting just get black screen with mouse curser.  Will not go into safe mode only black screen.  Can however do option button and control r to get screens but nothing will get me log on. Disk utility is not showing errors.  When it does go from apple grey screen to black screen it does show a little something on the screen then goes to black page.  I did get it on video but dont know how to put on here.  Please help.  Any suggestions.  Installed maverick on or about February 19th.  Would a board have gone out?  Any idea which one.  Not in warranty anymore. 

If you haven't found a solution to your problem yet, then here you go.

1.  Shut down your computer by holding your power button for 5 seconds

2.  Start it up and hold the shift button through startup until you see a bar

3.  When it gets to the black screen, type the first letter of your name and then hit TAB and type your password

4.  The rolling mouse should appear and the screen will go black again

5.  Hit the space bar and you should see an installation. Let it install and your good!

Hi aappleman

i have exactly the same problem. Tried everything, also your method but when hitting space bar, screen stays black with a faint light. i can see the cursor.

what to do???

THanks simon

Had the same issue and this helped! You're a life saver, thanks!!!

It took a few clicks but it works now!  The only thing is that when the graphics are slow to download when I switch desktops.

Thanks aappleman!!! This was extremely helpful! I was in a panic that I would have to dish out big money to get this fixed! You're a life saver!!!

Thank you so much that worked for me too!!! I tried everything before this. My sound doesn't work now and some of my screens do a strobe light type of flash. It's better than a black screen though. Any advice on how to get sound back and fix the scene flashes?

Sam

I Am also having the same problem . I have a 27" IMac . I have updated to OSX Mavericks . goes threw start up then goes to the black screen with mouse . Contacted apple even tho its out of warranty with Apple care . I have spent close to 3 hours over the phone with them the past couple days . Tried command after command . sat we re downloaded the OSX mavericks onto the iMac . Same problem again . Last night erased the hard drive and re downloaded software . Then went to go to re backup from time machine . It then told me there was incompatible software I'm guessing from the time machine ? Going to call later this evening to see what else we can do . The apple tec told me that there computer people are working on a resouoltuion to the software glitch . She said most computers come back going threw the 1st couple of techniques . And some just don't want to . I'm guessing I'm the lucky one . With a 2k paper weight !

Thanks aapleman! Your advice worked and all I had to do was wait patiently. I was a little skeptic at first to if it would work or not, but it's doing fine now!!!

I got this problem too - after upgrading my early 2008 Intel iMac to Yosemite.

I tried all the tricks in this thread and got nowhere.

The only thing I found that could get be logged in was to use Command-R at start-up and then reinstall Yosemite over the web.  But this takes many hours and was short-lived because the black screen would reappear next time I logged in.

I then had a long conversation with Apple support where we tried all the tricks again, but none worked, until they suggested the following:

1. Use Command-R to reinstall Yosemite

2. Log into computer and back-up everything to Time Machine

3. Restart with Command-R again

4. This time, go into Disc Utility and erase the entire hard drive

5. Reinstall Yosemite on the clean system (i.e. don't select the Time Machine back-up)

6. Restart computer

7. Computer will start-up with clean system.  Select option to restore everything from your Time Machine back-up.

The above took me several days dues to the amount of downloading and back-up, but has done the trick.  Operating system works fine now, with no black screen at start-up.

This is a terrible problem, so good luck!

Just restart the computer. I had the same problem.