Problem Reinstalling Yosemite

Have you tried booting into Recovery Mode (Command+R) or if your Mac came pre-installed with Yosemite, Internet Recovery (Command+Option+R)?

tanachfrombankok wrote:

"An error occurred while preparing the installation. Try running again" shows up when i try to reinstall. Think it started when i used a bad "clean my mac" app and deleted some other files. I set it to "set date and time automatically" on the Date and time preference but it still happens.

tanachfrombankok wrote:

I tried to reinstall Yoseminte because i cant access quicktime, photobooth, "about this mac", terminal, etc. but "An error occurred while preparing the installation. Try running again" shows up when i try to reinstall. Think it started when i used a bad "clean my mac" app and deleted some other files. I set it to "set date and time automatically" on the Date and time preference but it still happens.

CleanMyMac is one of the worst pieces of crapware around. It's borked many Macs. Be sure it is completely uninstalled.

http://macpaw.com/support/cleanmymac2/knowledgebase/how-to-uninstall-cleanmymac- 2

http://macpaw.com/support/cleanmymac/knowledgebase/how-to-uninstall-cleanmymac-3

This Apple Support Topic should help:

Apple - Support - Downloads

https://support.apple.com/downloads/macos

A. Restart and see if it continues the install.

B. Hold down the Option key from the “Purchases” menu in the Mac App Store, this causes the “Pause” button to turn into “Cancel”

C. If it doesn't go to your Applications folder and start "Install OS X" installer.

D. Hold down the Option key from the “Purchases” menu in the Mac App Store, this causes the “Pause” button to turn into “Cancel”

As long as you used your AppleID to download/install Yosemite when it was available from the App Store, you will still have it in your Purchases tab within the App Store.

So, you can use Internet Recovery to reinstall Mavericks after you use Disk Utility to erase your internal drive from the OS X Utilities menu. Then you can open the App Store / Purchase tab to download/install Yosemite. You have to erase Yosemite from your drive first to remove the error you are currently seeing trying to install Mavericks over Yosemite.

You didn't mention if you were able to use Recovery Mode (Command+R) which should put you into Yosemite's Recovery HD if it's there.

Computer memory is RAM not hard drive space (Storage).

You will lose everything on your internal drive when it's erased. So, it's a good idea to try to back it up somehow. Do you have a current back up of your data from Time Machine or some other back up method?

Correct.

There is one other thing to try before you erase and start over.

If you are able to get into Yosemite to do a back up then you should be able to download it from the App Store / Purchases tab. I'm assuming you previously downloaded it. Then run the Install OS X Yosemite.app file from /Applications. This will ONLY install the OS on top of itself and not touch any of your data.

But, if in your original post you already tried the above paragraph, then your best solution would be to erase your internal drive and start over.

One last long shot you can try. Try running the combo update. It installs all previous updates plus the new one, which can replace any files that may have become corrupted.

10.10.5 Combo Update