Why is that sometimes if I press F5 to play a song, the program hangs and just says "compiling" at the bottom.
Look at https://forum.noteworthycomposer.com/?topic=532, but I think the last (1.52a) NWC corrects this bug (since there has been a release since May).
You may have a problem in your notation, such as a series of repeat marks that create a song passage that repeats forever. You can correct the notation, but you may be able to prevent the problem by getting the latest release of NWC (1.52a). If you still have trouble (when using 1.52a), you can send us a copy of your file, and we will identify the cause, and add preventative measures to NWC.
See also: https://forum.noteworthycomposer.com/?topic=532