What is the most difficult computer troubleshooting problem you encountered?
Mine was actually just a few days ago! I was performing a clean install of XP on a new desktop system I bought (well, new for me..used off of eBay :) and I had to manually install all of the drivers..problem is, the "order" to install the drivers from Dell doesn't list the mouse until 5th or 6th..so my mouse wouldn't work :P Which means, I couldn't even restart or do anything. I was stuck. I had to call tech support and revert to a restore point to get my mouse going again!
In my history, they were all with windows. Computer are my job and I have to tell you, troubleshooting Windows computers are always a pain in the neck.
When they work, they work, but when they don't you may as well wipe everything and re-install again.
This is why I have 4 Macs at home now. As a professional, I simply do not have the time to waste fixing Windows computers anymore. Could not be happier!