27" iMac won't boot past white screen.

Unplugging everything worked for me. I think the culprit was my ipod for some reason... go figure.

Unlike others when I couldn't get past the white screen, I was able to boot via the option key and it gave me a choice of my 500GB drive or Recovery. I chose my internal drive and it booted fine. So, I knew there was something else that was the problem and not the drive itself.

Unplugging took care of it and I've rebooted several times with no problems.

Thanks for your help on this....

Gary

I got this white screen problem after having used Apple TV with my iPad. The screeen on my 27" iMac turned first gray then white and I couldn´t get pass the white screen. After having tried different suggestions I found on the net I turned the power off of my iPad. Prior to that I had also removed the power cable of the Apple TV box and all other cables from iMac. It was the turning off the iPad that made the difference ! The iMac started normally after I rebooted it.

My iPad is set up to synchronize wirelessly.

This suggests that there is some issue connected to the simultaneous use of Apple TV-iPad-iMac.

This solution seemed to be a quasi solution. My iMac has now started to freeze continually with a white sceen (some times it stops with a grey green, screen with narrow grey stripes, but each time after rebooting I come back to a white screen). I can use it only for a short time each time and it has been difficult to get back. Have tried several options I've found on the internett and my own but so far nothing has resulted in a permanent solution. This may be a hardware problem but all evidences don't yet support this. Need to continue with my problem solving and get back with the solution if I find any. If anyone has suggestions, they would be greatly appreciated.

Have you tried disconnecting all USB devices? I tracked my problem to a cheap USB hub.

Yes, I have tried that too several times but it has not resolved the problem. I have tried also powering off the time machine and tried to avoid any interferance with other external devices connected wirelessly to my iMac. But still I got the white screen. After several attempts of restarting I was finally able to reboot the iMac successfully. Now I have closed down all programs and try to proceed progressively. I downloaded the ClamXav virus program and am now scanning my iMac.

So far I have been able to use my iMac for a couple of hours. It is the record so far in the past two days 🙂. The last time we got kicked out was when my son was playing Minecraft in full screen mode. For the time being I've closed this program. There could be some connection which I need to check.I have probabably got the white screen about 10 times in the past two days. This all started this past week or so.

My CPU diode temperature is around 65 C and shouldn't be too high. The other temperatures are somewhat lower. So it doesn't look that I have any temperature problems (at least so far).

This is quite a mystery and very annoying when everything just freezes.

The problem was a defect graphic card. This is now replaced and everything works well 🙂.

Hey man, i had a same issue, the way to fix this:

1) turn of your Mac.

2) disconnect all of the external devices. (i had mouse connected)

3) hold down C( to boot using instalation CD) or Option key(to choose what u booting in)

4) Enjoy

i hope that will help u )

I just wanted to say thanks so much for your expert advice. PRAM reset was the only thing that worked so again, big thanks genius!

I don't know why my machine got into this state, but here's the "how":

Screensaver -> Sleep (timeout) -> [wakeup by keyboard/mouse activation] -> No response -> [hit power button] -> [white screen]

Restting the SMC worked for me. Thanks to the community for posted answers.

I want to contribute with an interesting solution. I ran the imac horizontally and it worked.

My problem was my imac wasn't showing any signs of life on the white screen after apple logo during boot. I also got black screen prior to the flashing blue screen in safe mode. No other solution worked for me but this. I was trying to see the serial number in order to identify if my imac if it's one of the 2011 models with defective AMD Graphics card. while i was trying to see the serial number i accidentally pushed to the power switch. imac has turned on while it was horizontal on my desk. now it works.

I assume it may be some dust was causing this. When i leveled the imac on desk i probably shook the imac's dust off the motherboard. So my suggestion is to shake and gently hit your imac in ddifferent positions. for example, lift your imac an shake back and forth, tap to the backside when it is horizontal so you may drop some dust from motherboard. you even maybe want to turn it upside down and continue shaking and tapping.

I hope this will help someone.

Like many others, my 2011 27" iMac wouldn't boot past a white screen. I tried all the solutions suggested here, but the solution, for me, was totally different. It turned out to be a faulty, but still operating perfectly, powered USB hub. Once disconnected, the boot process went perfectly

I found it was my USB3 TM ext. drive. I fixed the issue by turning off my Mac, then turning off my TM drive. Then power up TM drive then power up my Mac in that order. Any other order would not work. Now boots normally and no white screen hang up.

I have a thunderbolt drive that makes my computer crash on a regular basis. I have spend many hours with Apple Care.

I bought the drive in the Apple Store for back up...I would have thought that they would support this device but it seems that it does not work well.

Following the advice on grey screen solved my problem. But this happens all too often.

worked for me!!!!!

I have a 27 inch 2009 i-mac that goes to a white screen during use and during start up. At start up, the i-mac seems to go through the normal boot process, That is: Apple logo, the progress bar will display, it updates to the half way point. At that point, the display flashes and then the progress bar disappears. But the hard disk continues continues to make noise as if it is still reading data. The screen is white but the mouse can control the cursor. I took the i-mac to the local Apple Store and they determined that the HD was bad. After replacing the HD the machine worked for a day. Then as if to make up for lost time, the i-mac white screened three times in one afternoon. In addition to a new HD, I have tried replacing all of the memory DIMMS, running the internal fans at higher RPMs, removing all USB devices, unplugging the i-mac for a day, connecting an external display, & booting in safe mode. This has been happening more frequently but it is still an intermittent occurrence. I can see why some of the "solutions" here seem to have solved the problem.
What was the verdict with the video card replacement? Did that solve the issue? There are some faint 1 pixel wide vertical lines on the display at times. Does anyone else have that issue and could there be a connection?