Today I had to reformat an old laptop with Windows XP.
After doing this, there was a 'loop' on the authentication process. I know what you are all thinking, but it was a genuine version.
What this meant was it kept asking me to authenticate it, and then telling me it was authenticated, all the while stopping me from going to the main start window.

I rang Microsoft. What a joke. After having to explain to the 'service technician', who quite frankly I knew more than he did (which is saying something) he gave me three options. Go to service technician, reinstall it, or pay $80 to be transferred to the next level of service help....sigh. I politely thanked him, but informed him, nicely, that he was no help.
A half hour of googling later, I installed Service Pack Two, and the problem went away.
The laptop is now working.

Mmmm...the internet tech support community is free...if you look hard enough, and much more helpful than Microsoft....