When the customer fisrt turned the machine on, the system would would light up and the fans would turn on, but it would neither POST nor boot into Windows. After some investigation, I found that I would need to run a repair installation of Windows in order for the machine to boot into Windows properly.
I did, and Windows did. But, the problem persisted, even after the scanning mentioned above.
It was at this time, that I installed all of the customers recent updates and the newest version of Internet Explorer, as well as the Firefox browser. This appeared to fix the problem.
After a couple of reboots to check for proper operation, it turned out that the problem was not remedied.
This problem could be gotten around by using Firefox(which I always recommend), but, because this was merely a work-around, the customer was not happy.
Normally, this is when I tell people that they need a format and re-installation of Windows.
Formatting erases the hard drives and all problems associated with Windows. Sometimes the situation is so dire that none of the customers data can be saved.
This was not one of those times.
The lesson I have learned from this experience, is that if your computer needs a repair installation of Windows just to get it to turn on, you need to save all of your data immediately and then format and re-install.
And why werent you performing regular backups of your data anyway?