There are probably different reasons why the "Preparing automatic repair" problem appear so that you cannot boot to windows 8.
In my case however I found that removing the usb cable connecting to an external drive solves the problem.
Let me elucidate a bit how I came to experience this problem. I was repeatedly prompted by windows in my Toshiba notebook to upgrade to windows 8.1. I thought it should be a better version - like it will make my 32bit programs run faster - otherwise why keep prompting. I was mistaken by this irresponsible hype of Microsoft.
After upgrading to windows 8.1, I could not even open a table in an 350mb MsAccess database with the error that goes something like "ODBC run of resources" when previously it was not a problem. And I have 12GB of Ram in the notebook! And yes I know not all of that RAM is allocated for a 32bit database but still I read it is something like 4GB for 32bit.
In fact my other notebook -- an old HP with XP running on 1.25GB of Ram has no problem at all opening the table in that large database.
Another thing happened when I upgraded to windows 8.1 -- m y HP Laserset 1020 driver was removed during the upgrade without any warning. When I re-install the driver the printer fail completely to print.
Because of these setbacks I restored my Toshiba notebook to factory settings taking several hours for this job to be done. Boo, Microsoft should improve on this.
After restoration, the notebook got stuck in the "Preparing Automatic Repair" mode during reboot. I scoured the Internet for an answer. I tried removing all cables and battery and let the notebook rest for at least 15 minutes. Still the problem persists.
Then I tried this : Before bootup I remove all USB cables. The notebook then boots to windows properly. What a relief. Now I have nailed the problem down to the usb cable connecting to an external drive (which has a previous XP OS in it, is this a problem?). I surmise I should therefore go to BIOS to look at the boot order.
It shows the internal harddisk is the first in order. Even after moving the external drive to the last in boot order the problem came back if I do not remove the usb cable to it during bootup.
Perhaps this OS bug "Preparing Automatic Repair" may have something to do with the BIOS attempting to read an external drive as a bootup drive and hence reporting this error if that OS in it is not a working one and hence attempting to REPAIR it, I am not sure but hope it provides some hints for Microsoft to resolve this crazy fatal bug.
As to why previously before the lousy windows 8.1 upgrade there was no such a problem is something beyond me.
Anyway give it a try, remove all usb cables during bootup and see how it goes.
In my own case now I know what is causing this crazy "Preparing Automatic Repair" freeze-up. The OS is doing a chkdsk on a drive. In my case it was an external drive but there was no indication the actual chkdsk process was taking place given that it was only 'Preparing ...' oh great.
After successfully booting up to windows - as per my solution above - I now solve the problem by going to command prompt and typing chkntfs /x g: where g: is the external disk. If the external disk is partitioned you need to also run the statement for the other partition e.g. chkntfs /x h:
You can do it for both partitions at the same time eg. chkntfs /x g: h:
After that reboot with external disk still plugged in and the system will boot to windows without any problem. So 'Preparing Automatic Repair' does not necessarily mean your main harddisk has failed and you have to send it your PC to the factory for servicing.
I think this 'Preparing Automatic Repair' message is misleading as it tells us very little what the system is trying to do. This is not clever at all as with many new offerings from Microsoft, it is just making things hellish for countless users.
