I have erased my HD and tried to install OS Yosemite on MacBook Pro mid 2009. But keep getting this message "This item is temporarily unavailable." I've tried many proposed solutions but none seem to work. Any one experienced a similar problem?
Let me preface this: it's possible that this solution doesn't work entirely, and that you'll need a version of the installer that has a full copy of OS X (instead of downloading it from the internet on the fly.)
With that said, here's the issue. Your Apple ID (and therefore purchases) are not associated with the computer you're trying to install to since it's a clean install. Therefore, it doesn't know you've "purchased" Yosemite previously, and since it's no longer on the app store, isn't giving you access. What you need to do is reassociate your Apple ID with that computer. The recommended solution is to log into icloud.com.
Alternatively (or if that doesn't work), you can download it from another computer with a working version of OS X and then execute the installer from there (or create a bootable installer from there.)
Small side question: why not install El Cap?
Checked that you're Apple Id is connected to the correct App Store region.
The easiest way is, in App Store, select go Store > View My Account ...
A check will be made if the App Store region will be checked, and, if they're out of sync, at this point, the correct region for your Apple Id will be selected.
After this point, you should be able to install apps and updates from the App Store.