If your computer is in the bedroom you can find many restful sounds , music to sleep by, relaxation sounds - any of those searches on YouTube should bring up many to try.
just find some that you like and try them out
some are short and some are longer but the length is posted for them, so a longer length one is what you would look for.

There are a few websites that you can even set to play rain, thunder, waves sounds all night long.

I've used this one for just relaxing-
just set the sliders on the drop down menus for the sounds you want and how loud you prefer.
http://www.soundsleeping.com/