Since you can start programs in the task manager, go get EVENT VIEWER running (see http://www.google.com/search?hl=en&q=VISTA+EVENT+VIEWER&btnG=Google+Search&aq=f&oq= ) and hope it tells you something more you can use to further your research.
You can also launch system restore (noted at http://www.google.com/search?hl=en&safe=off&q=VISTA+COMMAND+LINE+SYSTEM+RESTORE&btnG=Search ) if Safe Mode is failing too.
I apologize for the length of this post, but I wanted to include the most accurate information that I could. I am running Vista Home Premium on an Asus P4P800E-Deluxe MoBo, Intel P4 3Ghz/4GB, HIS/ATI HD 2600-XT 512Mb.
After a cold boot, the system comes up to the logon screen and is normal to this point. After login, the screen goes black with only the white arrow cursor (again normal). However, it never displays the Desktop, Start button, Task bar/Tray or Side bar. Just two black screens. Right clicking does not produce a menu and the system is unresponsive.
A three finger salute does bring up the screen allowing me to load the Task Manager, which I can then move to either screen. In reviewing the loaded processes dwm.exe is loaded as well as most other essential processes as compared to my laptop (running the same version) but explorer.exe is noticeably missing. If I try to manually start explorer, it will flash on in the processes screen for about ? second before disappearing.
I have been able to load any other programs I have tried, but must do so through the Task Manager with the Run cmd. I can also start system level programs by running a command screen. In short, the system runs fine except there is no Desktop and everything must be started manually. It's interesting to note that when I start a new program by using ?Run/Browse? explorer does function properly when started internally.
I have performed diagnostics and have even run sfc.exe in an attempt to correct the problem with no change in results. I have also checked the following registration entry:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon and the shell string is set to explorer.exe.
I have also run Boot Log and did not find any smoking guns. In searching tech forums and Microsoft's TechNet, I can find no reference to a situation such as this. I am convinced the problem resides within the Registration file, but have no idea where to look. What I obviously want to avoid is reinstalling Vista and having to reload all of my programs.
Any ideas would be greatly appreciated.