Black Screen with Mouse pointer!!!

Windows Vista 32bit sp2(Main OS)
Windows 7 SP1 32bit(secondary OS)
Intel C2D E8400
Transcend 4GB Ram DDR2
Sapphire ATI 4770 HD
Seagate 250GB
WD 160GB
I was facing this black screen with the mouse when I logged in.Then after surfing the net,I found it is called the Black Screen of Death.I tried the Prevx fix by accessing the explorer.exe through the Task Manager.Nothing Happened.I tried 3-4 times.

I have tried registry Fixers and cleaners.Still nothing happened.
Whenever I click on My computer which I have accessed thru explorer.exe.It shows That explorer.exe is not associated with any program and I need to provide a program thru Default Programs.

I tried a registry fix called explorer.reg from the net.Nothing Happened.I tried the SFC /scannow command from the Command Prompt with Administrator privileges.I showed it could not fix all problems.It just changed my logon screen to the default blue one.

I also tried the Repair Install as given in your forums.But it showed that my Windows is more recent.I have attached the compatibility report as PDF.I think its because I have Win 7 SP1 installed.
Then I tried to remove SP1 form the updates.I couldnt do it by any method starting from the Installed updates page...then through Command prompt and also Disk Cleanup to remove the Service Pack Backup files.It is always showing an error of corrupt files or something.

I have tried accessing it thru Safe Mode and also Last Known Good Configuration.It still shows Black Screen with only mouse pointer.

One big problem is that I cant seem to find any System Restore points so I couldnt do thru System Restore.
I also tried Start Up repair.But this also didnt help.
Please help me as I don't want to do a clean re-install as I have lots of games in it(even though I can copy their save games).I want to format as a last option.

I got something similar to that once and I had absolutely no idea what to do. The way I got around it was by restoring the system from a system restore point, which thankfully a program I installed made just the day before so I lost almost nothing. I don't know if your problem is exactly the same, but the system restore point worked perfectly for me. Press F8 or F5 (Can't remember which) as Windows starts to get to the options menu and choose system repair, and there should be an option for system restore on the options menu it will provide. Sorry if this doesn't help, then I got nothing except maybe putting the HDD in another computer and backing up important files that way, then doing a clean install of Windows.