Hi Bob welcome to the forum

Have you tried running msconfig and disabling all startup items to see if one of them is the cause? COuld very well be somthing in startup stopping it.
How to use MSCONFIG in Windows XP
Here is how to use MSCONFIG in Windows XP to disable some of the unnecessary programs that automatically load on start-up. Disabling these programs will help your computer boot faster and crash less. [For step-by-step instructions on how to use MSCONFIG in other versions of Windows, please visit my main
How to Use MSCONFIG page.]
1. In Windows XP, go to Start > Run
2. Type MSCONFIG in the "Open:" box and then either press enter on your keyboard or click on the OK button.

3. This launches Microsoft's System Configuration Utility. Click on the Startup tab (the tab at the far right).

4. This takes you to a page with a list of "startup items." Startup items are programs that are automatically loaded every time you turn on your computer. Some startup programs are absolutely necessary, others are simply a waste of
RAM. Disable all and click ok the PC will reboot
Will the scan run now?