I wanna share my experience when repair/troubleshooting computer when i was working as computer technician . Sometimes when I troubleshoot computer I got stuck,because i can't find cause of the problems. This what I do, I use this diagnostic chart as my references. Example like picture below (source from Fonerbooks.com):This is the diagnostic chart for Power Supply Failure. It show what to do if you stuck at some part.
Maybe it's no 100% correct but you can use it as a guide. I recommend it for beginner who wanna to try troubleshoot computer. You can get other diagnostic chart from here.