when I hit the play sound block nothing happens! I don't know what I have to do to make it work.
You not mute sounds in browser or device?
I tried everything I can think of.
Hmm.... It must be device problem.
maybe but I don't know what.
Try reset computer. For sure it isn't:
done that
and the same?
Please give your device stats. There is some problems with Mac Browsers not playing sounds.
thats the problem then. I use a Mac
You must be a Windows user. ;~/
Where did the sound come from, and in what format is it? We rely on the underlying sound support in your browser, and not all browsers know how to play all formats.
I'm not
sometimes it happen me, and this a problem with what I connected drivers 
well I don't know @snapenilk gave it to me. I don't know what format. like I said it was given to me.
Ah. I said it because "reset the computer" is the standard thing Windows user support people always say. :~)
It's a file on your computer?
No:
It's a sound in a project.
I got the music from Incompetech (which I am very familiar with; it is completely safe and even works cross-origin, e.g. in my Royalty Free Music Repertoire), but I used an MP3 compressor that I haven't used before (see I need music!). The compressed MP3 files (and the original) played in Snap! for me, so I think the issue is in SirHopsALot's computer or browser.