This technique of troubleshooting is one of the last things I try when working on a troubled PC. The reason I try it last is because it is one of the slower ways of troubleshooting. Since it is usually the last thing I try I will share it with you in case you are at the point where you have already tried everything else. The Ultimate Boot CD is my tool of choice. I will also sometimes use BartPE but I am still not comfortable with that one yet. UBCD comes preconfigured and is very user friendly. UBCD allows you to boot into several different modes. Here I will tell about the diagnostic tools it is equiped with.
When you boot up with the CD it will load very similarly as Windows XP. Once it finishes loading, again it will look similar to Windows XP. My favorite part about the UBCD are the spyware/virus tools it is pre-loaded with.  The only real problem with the UBCD is that the virus/spyware definitions go out of date and there is no way to update them so you have to frequently make new UBCDs to keep up with possible new viruses/spyware.