Solved Cannot get into Windows 8

I have been running Windows 7 and 8 satisfactorily on two separate partitions on the same hard drive with both of the preview versions of W8. Yesterday I bought (online) and successfully installed the complete release version of W8 and all was fine.
Today, I decided to increase the size of the W8 partition (and decrease the W7) using MiniTool Partition Wizard. This seemed to work OK but when I enter my password for W8, all I see is a message saying "Preparing Windows" but nothing further happens. W7, in contrast, works perfectly and I can read the files in the W8 partition using Explorer.
Any help and suggestions would be very welcome.

Win8 might have decided to change it's drive letter.

If you can get into 7 ok - fire up regedit, load win8 system hive and change it back to whatever it was - C if you installed by booting the media.

If that is a bit complicated :

If you already have a Paragon program you can just use the boot corrector module from that - it is very easy.

Or you can d/l the free Paragon rescue kit express, burn it cd boot it up , select Normal Mode >Boot corrector>Search for windows installations >Correct system drive letters.

Rescue Kit Free Edition - CNET Download.com

SIW2
Many thanks for your suggestion. In the end, I downloaded the setup iso to a USB flash drive and reset my PC from that. All now appears to be working correctly with W7 and W8 in tandem. I think your idea about drive letters changing may haave been correct but I had embarked on my own course of action before I read your message.