Process explorer

It is imperative to know what processes are running on your computer and what they are doing. The standard tools provided in Windows gives some help, but they are very rudimentary. Process explorer is a great tool that Microsoft provides for free which provides much more detail about running processes. Process explorer let you see a great deal of info about running processes, for example, which files or directories a process has open and which DLL-files a process has open. Great for tracking down what an application is doing or if there are any problems with DLLs or files for example.

http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx