WhatIsHang is a tiny tool that can help you find out why some programs freeze and become unresponsive.
When you notice that a program seems to have locked up, and WhatIsHang should detect and list it in its top pane. Then click File > Get Hang Information (or press F9) for WhatIsHang's analysis of the cause.
The author points out that WhatIsHang is "designed for users with Windows programming knowledge", and that's true: it may ask you to do things like "look in the call stack", which won't be particularly useful advice for most people.
However, even in a situation like this, the program will list strings found in the stack, and even if you've no idea what the "stack" is, that could still be useful. You'll see file names, for instance, which might indicate what the locked-up process was doing when everything went wrong.
WhatIsHang can be very useful, then, and may at least offer some clues as to the source of the problem, but please note, there are some potential gotchas.
In particular, on Windows Vista or later with UAC enabled, WhatIsHang can't detect broken apps if they have system or administrator rights. So if you see nothing, right-click the program executable and select Run As Administrator to try again: that may fix the problem.
?Fixed bug: WhatIsHang failed to remember the last size/position of the main window if it was not located in the primary monitor.
?Added 'Run As Administrator' option (Ctrl+F11), which allows you to easily run WhatIsHang as administrator on Windows Vista/7/8/2008.