Moo0 SystemMonitor lets you keep your eye on system resource usages of your PC. It currently supports 36 kinds of information including CPU, Memory, Network, and detailed HDD usages. Using this software, you may discover what is limiting your system performance in each occasion.
The program uses a minimal amount of ressources, and you can learn from it where your computer "hangs". You can see your computer under many perspectives, and with the features you can diagnose your computer. You can have as many features as you want open and have them in the way that fits you best on the screen. I use Moo0 SystemMonitor every day.