A few days ago, I installed Service Pack 2 despite all the software it keeps from functioning properly. It was on the family PC and so I thought that the added security would be worth it. (they're not the most careful on-line)
After the install my computer restarted and started booting. Then it restarted and started booting. Then it restarted and started booting. Then it restarted and started booting. Over and over again.
First I put the HDD in my computer and started Linux (of course). I went to Microsoft's web site and after an hour of looking I found out that this is actually a common problem. So I looked at their solution, which actually included starting Windows and starting a script full of copying and deleting files. Since Windows wouldn't start, I spent hours changing every "c:\...." to "/mnt/hdd1/...", "copy" to "cp" etc. not to mention all the "\" to "/" (i was saved by the replace function in the text editor). I quadruple checked everything and let it run.
An hour later, it finally finished. I look at all the output to make sure all the files were deleted or copied. I put the HDD back into the family computer and started it up....... and BAM! "Welcome to Windows XP" flashed up.
Moral of the story: "You know your Operating System is better when it can fix the mistakes of another!"