could be a bunch of things. Until you do a little trouble shooting, we won't have any direction to start.
BUT... if it was my boat... I would start with the basics.
1) check the spark plugs, and replace.
2) check the fuel system, and clean the carbs.
Also... would it re-start? When it died, was it a bog, or was it instant (like throwing a switch) A bog is normally fuel... and instant is normally electrical.
Give use a little more info, and we will get you through the issue. :cheers: