Exact same issue. I have had this happen with one other program (Windows Live Essentials 2011) and have never found a good fix. Booting to Safe Mode and choosing restore point created by LogMeIn install restored the login screen, but of course without LogMeIn.
This issue was first noticed with a few of our users in our UK office. I am now able to 100% reproduce this issue by doing the following:
1. Start with our standard US Win7-64bit install. LogMeIn install works properly at this stage, through multiple reboots and login. 2. Change all localizations to UK 3. Install LogMeIn, restart 4. Login screen has only Cancel and Shutdown button after ctrl-alt-del.
I can achieve the same thing by installing LogMeIn *before* changing localization to UK - problem returns after restart.
Finally, here's something really interesting. I took the standard image, changed localization to UK, restarted, changed it BACK to US, restarted, then installed LogMeIn. Blam! Same issue. Something was permanently altered by changing locale.
Because changing localization has so many components (format, location, keyboard, welcome screen, new user template, system locale) I have not yet tried changing one at a time to see what happens. If I do so I will post here.
I haven't found any clues in Event Viewer. I found this old 2003 article for Windows XP that sounds similar for a problem caused by PCAnywhere, but it doesn't apply to Win7. There's nothing in they key indicated (HKLM\software\Microsoft\Windows NT\CurrentVersion\Winlogon) that seems relevant. http://support.microsoft.com/kb/817142
There was a subkey to Credential Providers named with a typical random name (curly brackets with hex digits) and a string value of "LogMeInCredProv" (without the quotes). There were no other sub-keys to Credential Providers, and another Windows machine of ours had no sub-keys.
Removing this key brought back the normal Windows login - terrific! Not sure what effect this will have on LogMeIn - I did try remote control with no user logged in, and I was able to control and log in to Windows with no problems.
I wonder if this is a 64-bit issue, I discovered the following post after your idea above. I'm going to do more research on this. LogMeIn has x64 and x86 folders (both within Program Files (x86), oddly) but perhaps it's not being called properly by the welcome screen.
Regardless, this is great - even if it makes install harder (have to fix registry before restart/logout, or go to safe mode to do so) at least it works. For my remote users who don't have it yet, I'll walk them through install on the phone or chat, then immediately connect to their systems and remove the key before they log out or restart.