I clone my drive and then I can try whatever I want on the clone with no fear of wiping out. And I can try it over and over.
Only Microsoft can fix those CDKEY and validation errors so be sure to set enough time in the day for that call.
In closing, I find many users blissfully unaware of a few things. Let's get them up for discussion.
1. Cleaning your PC or laptop -> http://reviews.cnet.com/4520-11319_7-6240575-1.html
If you are running a business without backup, that's your choice but it never helps when folk discover there was no backup copy.
When WIndows Vista crashed and burned, ruining my hard drive I decided to install the evaluation copy of Windows 7. Once the version was officially released, I purchased an Update copy and entered the Product Key into Windows Activation. The key was accepted, and everything was cool for the past year. Since then I have installed dozens of applications and also use this system to support my web design clients. Now, suddenly I am being told that the evaluation copy has expired, and get blue screen crashes based on that. I can't "upgrade" since the installed version has had all the Microsoft updates and is consequently more recent than the purchased dvd. Is there any way I can avoid a clean install? I'm not sure I'll be able to reinstall all those applications, most of which were electronically downloaded, not physical media.