Grey screen on restart after Yosemite upgrade !

Well, whaddayaknow -- turns out my SSD bit the dust. 😮 Apple was kind enough to replace it at no charge. Thank you, Apple!

Thanks Sparkleberry, in safe mode my iMac continued to download Yosemite even though I downloaded it when it was first released. I then restarted and back to normal.

Thanks for the information. I have done the safe mode reboot and it worked to get my computer back to the normal screen.

Now the computer is super slow. Do you have recommendations on how to address the slowness?

Thanks.

Hi SubL. I found that I had a startup virus that intercepted my boot process and slowed my system down.

It would bring up "yahoo/finance" as my start up screen in Chrome. Maybe you have that little passenger?

I had three machines that I struggled with, when upgrading to 10.10.3.

All of them were iMacs (2 different models)

Each of them showed a gray screen with a mouse cursor that indeed moved when I moved the mouse.

I tried a little bit of everything trying to get this fixed on each of them. Including most of what I read on this thread.

Zapping P-ram

booting in safe mode never seemed to work

Running repair disk (Command-R at boot)

Etc

On two of the machines I ended up reinstalling an Older OS (10.10.2) and was then able to upgrade these configurations to 10.10.3.

The third machine was not critical, so I've spent time with it.

and eventually, I found that I could ssh to the machine, so it really was up.

I thought perhaps it was thinking there was another monitor, so I connected another monitor, and immediately a screen saver kicked in and then went away on the main monitor (iMac screen) on the external monitor, I saw the Yosemite background, and then got the login prompt on the iMac screen.

I do not know why zapping the p-ram did not solve this issue, and I'm not sure what to do if you don't have another monitor laying around, but this solved my problems.

Hi, I've tried all of your ideas and none work. Every time (about 50 times in the last week) I go to re boot I just get a grey screen, no cursor no nothing...Prior to the download I had done a deep clean of my hard drive and loaded up Mavericks. I then started the Yosemite download it seemed to die out on the restart and I tried rthe various key moves and nothing still a grey screen. Any other thoughts? I would be happy to go back to maverick but I cant get to safe mode, disk utilities or the thumb drive Maverick is on

I had done a deep clean of my hard drive

how did you accomplish the "deep clean"?

disk utilities. erase disk. set it to the longest time for a multi layer clean...it took about 16 hours to erase it. I the ned up from thumb drive that had mavericks and installed at. It worked fine until i decided to do yosemite install

been panicking for 2 hours worried about all the data, found this website and the first solution worked!

Thanks!

What happened to work for me, is that I just held the SHIFT key down from the moment I started the MAC and didn't let up. It worked, maybe by accident? It did not go into safe mode, it just worked?

After trying everything under the sun i did this at the frozen grey screen and i got my company's security popup then finally got into the login screen. Thank you very much

TThank you so much! That worked for me!

I didn't have a grey screen but very strange over intense colours when logged in. After trying calibration, colour sync and other things, I fixed it by going the settings/accessibility/display and resetting the display to normal as it was on maximum (the source of the over intense colours). This problem had been interment before upgrading to Yosemite. I had delayed an Yosemite upgrade as it might have caused problems with my Chemical Drawing Package (ChemBioDraw 14.0)

I hope this may help others with colour problems; have a look at accessibility settings.

Cheers, Ian