Can't install Mac OS after installing Windows, Can't install Mac OS after installing Windows

Restart you computer by holding down the option key, is should give you a menu to start with Mac OS or Windows.

Try starting your system in single user mode, then run fsck on your hard drive, take a look at this link, http://support.apple.com/kb/TS1417

Try press the F8 when starting, this is for windows only. you may need to press FN + F8.

It sounds like your EFI firmware got hosed, it contains the initial boot screen (gives white if it doesn't load) and also controls the at boot key commands on a wired or built in keyboard (wireless doesn't work)

EFI resides in a hidden partiton on the boot drive and is loaded into Non-volitile RAM upon boot to be ran on the next following boot. So if the data on the boot drive is gone or corrupted, so the next boot you don't have your EFI firmware in NVRAM.

To fix this issue you will require another Mac that can burn CD's and know the EXACT model of your sick Mac to get the correct firmware.

https://support.apple.com/kb/HT1237

Once you have that file you need to burn it to a cd using these instructions and apply.

https://support.apple.com/kb/HT2213

Two reboots later it should be in your NVRAM and then you can c or option key boot and make repairs.

..Step by Step to fix your Mac

Create a data recovery/undelete external boot drive

ArnsteinK wrote:

This sounds like exactly what I have to do! Thanks A LOT!

It's a very rare occurance and I had it happen to me once in decades, so it's not like many know about it. 🙂

The firmware restore cd doesn't start, boot or anything visible on the screen, it just loads it behind the scenes, does the flashy or beepy thing.

Reboot twice and see if the at boot key commands work again using the OS X install disk, option key or command r or command option r while booting. (you never mentioned what OS X version or machine your using)

It's possible a recent firmware update occurred (software update or AppStore) and bricked your EFI, the version you get from the website download is older because they don't release it there until it's been tested in the field like on people like you. 😟

If a newer firmware is on the machine already and it's borked, the older one your using won't load, only newer versions are accepted by the hardware.

If this is the case, your only choice is to have the logicboard replaced, I hope you have AppleCare. 😐

You also could have made a mistake and downloaded the wrong one, so it's refusing to apply it.

Need machine/operating system identification help?

Find the serial number, thus the model number and thus gives the operating system that originally came with the machine. However gives not what operating system version the boot drive was later upgraded to. Do not use older OS X verisons to repair newer verisons. It is possible to use the original operating system version installed on another boot drive to recover files from a later operating system non-booting drive.

https://support.apple.com/kb/HT1159#MacBook_Pro https://support.apple.com/kb/HT1349

https://support.apple.com/kb/HT1559 http://www.everymac.com/ultimate-mac-lookup/