Solved Changed Win8 drive letter after partition change in EaseUS

[Atrejoe]

I used to boot into Win8 which has been installed on a partition with drive letter W.
After I ran EaseUS partion manager (Best partition manager software - EaseUS Partition Master Family.), the partition has been enlarged, and at first glance I am able to boot.

Unfortunately, my login screen is not customized anymore (does not display background pictures, apps et cetera), and upon login I can hardly do anything (no desktop is displayed, I cannot start an explorer instance et cetera). Guest logins are automatically kicked out.

Upon logging in (it has remembered by username, and apparently my credentials) it just says 'Preparing Windows' for some time, en then displays a blank screen, in which I can see my mouse, and with ctrl-alt-del get some options, but I'm not able to start the task manager.

When I reboot into safe mode (which is way more hidden than in Win7) I àm able to start a task manager, en from the I can run items, browse my PC et cetera. However, I can see that my drive letter has been changed from W to E. Most of the application I start are broken, like when I start the MSC snap-in in order to maybe change the drive letter using Windows' built-in partition manager, it state it is broken.
When I try to change the drive letter using the command prompt and 'diskpart', I'm not allowed, as the drive I want to assign a drive letter to is a system drive.

I seem to have suffered no data loss (I've got most stuff backed up anyway) but don't want to re-install either.
The system is dual boot, so I can work on the Win 7 version, but assigning a drive letter in Win7 only assigns it for the Win 7 instance.

Any bright tips anyone?

 

[Atrejoe]

Phew, found a solution myself:

With some effort I was able to boot into safe mode, tricked an instance of the task manager, from the task manager I could start regedit.

In regedit I assigned the appropriate drive letter under:
HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices

This worked for me, but I recommend this ONLY as a last resort kind of thing.