The key to troubleshooting PC problems comes in gathering all the necessary data. You could try to do that manually, running MSCONFIG, REGEDIT, various Control Panel applets, Task Manager and more, then manually noting down important points. But it's a lot easier to use LookInMyPC, which automatically locates and assembles all the information for you.
Simply launch the program, click Generate, and LookInMyPC will go to work, collecting the data you need. This includes real-time information on running applications, processes, and the users logged into your PC. Software-related data includes everything from the list of installed applications, to your service settings, Windows startup programs, antivirus and firewall programs. And there's basic hardware details on your CPU, BIOS, DVD, hard drives, RAM and more.
This report is presented in a local HTML file, generated by LookInMyPC, so you can easily save it for posterity. This means you could, say, create one report when your PC is working normally, another when there's a problem, and suddenly it's very easy to see what's changed.
LookInMyPC can also send the report via email, though, which makes it a very handy tool for diagnosing problems on someone else's system. Once they've installed the program, just launching it and clicking "Generate Report and Email" will get you everything you need to know about their PC, which could mean you're able to spot the problem without needing to be there in person.