I'm a tech support guy for a local municipality, and a high ranking person brought in his computer he was doing some work from home on with the same symptoms as you folks have described. I hooked it up and was able to get by the password screen with a blank password, but Explorer.exe would crash, causing the whole interface to fail loading.
Explorer.exe Application Error
Failed to initialize properly 0xc0150002
About an hour of Google research turned up several results of folks that have had this problem caused by a specific Windows update, KB923191. In this thread and other sites, folks recommended booting to Last Known Good Configuration or booting to Safe Mode with Command Prompt and manually uninstalling the update, both of which failed to fix the problem. Finally, I got to Andrew's post where he recommended a link that no longer existed.
I had tried the update uninstall via the Safe Mode with Command Prompt, with no success, and System Restore must be disabled on this machine as the restore folder under %systemroot%\system32\ doesn't even exist. Regular Safe mode would turn up the same logon screen and error box. Still no GUI.
So, I tried Andrew's advice. His page is no longer up, of course, and Google didn't cache it. But, we're in luck - the Internet Archive Wayback Machine has it still! - in fact, it has several versions of the web page.
The important part of the document:
This problem was repaired by replacing the following two folders from the same folders on another working Windows XP SP2 install (or a parallel install) without the patch having been applied:
Read/write access must be gained to the drive, which can be done through Microsoft's recovery console, BartPE, or another method.
The failure is almost certainly due to just one file in one of these directories, but as of 22/10/2006, I am unable to be any more specific.
I had to boot a laptop running the same version of Windows (XP Professional) into Safe Mode in order to be able to get these folders as, otherwise, they are locked. I copied them to the Desktop, and rebooted to copy them to a thumb drive. I booted the broken computer with UBCD (A light version of Windows that runs from CD) and deleted the bad files and copied over the good ones from the thumb drive. I had to use the thumb drive because the burnt CD I made first couldn’t be loaded while running Windows from the same CD drive. I rebooted, and the Welcome screen was back, where the user can click his user to log in.
The computer is now back to 100%, and the user has picked it up to take home. He was very pleased that I didn't have to completely reinstall Windows. Thank you folks for your assistance!