Hi George,
Are you able to boot to the desktop intermittently?
Let’s follow these methods & check if it helps:
Method 1
You may try to boot the computer in Last Known Good Configuration. It is a recovery option that you can use to start your computer by using the most recent settings that worked:
Using Last Known Good Configuration
Method 2
You may boot into ‘Safe mode’ and check if you are able to boot to the desktop. It will start Windows Vista with a limited set of files and drivers. Startup programs do not run in safe mode, and only the basic drivers needed to start Windows are installed, follow the steps to boot the computer in safe mode:
i. Restart the computer.
ii. Start tapping F8 key.
iii. You will get Advanced Boot Menu Option window.
iv. Select the option Safe mode.
Refer: Start your computer in safe mode
Method 3
If ‘Method 1’ doesn’t help, you may follow this link:
Note: In a clean installation, existing data is deleted. This data includes personal data and settings. After you install the operating system, you must also reinstall all programs.
Refer: Windows Vista and Windows 7 Black Screen on Computer Unlock
Hope the information helps.