re install yosemite

In most cases this is not necessary, why do you feel a reinstall of OS X is needed?

Okay, if you have data you want to save first back that up.

Next restart the computer in Recovery Mode by holding down Command + R

Next open Disk Utility and select the volume and click the Erase tab and Erase the HD

Next Exit Disk Utility and select Install OS X and wait until it's done.

Must have internet connection. May have to have your AppleID password. When you boot into recovery you will see the Wifi symbol on the upper right hand corner, click on that to to join network.

Hope this helps and Good Luck, Tom

JAYBOWL wrote:

Where does the Yosemite program for installation come from

From the Recovery Partition that is already on your HD. Just follow the steps and it should install without drama. EVISCERATOR is correct, you can also download it from the Internet however you should not have to, it is almost certainly on your HD.

Re blue flash screen, I have never heard of that. You can try to re-install as before from the Recovery Partition. Perhaps your install was corrupt.

You can attempt an internet Recovery as described earlier, if that doesn't take care of it then take it in to have a professional look it over.

HI JAYBOWL: A little more info is requested so that I might help you, so please; What year is your iMac? Is it a fusion drive. What OS came installed on it?

If it is a fusion drive then try this:

Notes: use command c to copy and command v to paste also the correct UUID string is the first one.

The steps I took:

• I booted from recovery mode (Hold 'Command' and 'R' while starting up)
• From the menu screen ... On the top bar I selected 'Utilities > Terminal'.
• This opened a terminal window.
• Then I typed: diskutil CoreStorage list
• And hit 'Return' ...
• This showed the main storage drive details.
• From there I found the UUID string ...
• Which is basically the long number displayed under the storage drive name.
• I selected and copied this ...
• Then I typed: diskutil CoreStorage delete
• Followed by the UUID string number ... And hit 'Return'.
• The system then erased the main drive (it left the recovery dive intact though).
• I then quit Terminal ... And went back into 'Disc Utilities'.
• Only to find all of the drives displayed individually and in red ...
• The 'Solid State Drive' and the 'Hard Disc Drive' were no longer displayed as one 'Fusion' unit.
• However ... Upon clicking on one of the drives ...
• The system recognised they were not unified ... And prompted me to fix this.
• I asked the Disk Utilities to 'Fix' ... And the system returned to its normal state.
• With the drives displayed as:

• Internal Drive • Macintosh HD

• I was then abl
• Good Luck, Tom