>>>Do a refresh on the page or close the browser and reload. External .js files are downloaded once to the browser and cached.
>>
>>I got the code working correctly from the ASPX page I'm working on, but why I can not use it from my Master.js and I was able to do it just yesterday?
>>
>>Could it be time to re-boot or there is a better alternative?
>
>Sometime later it worked by itself.

I prefer to develop the Javascript that is specific to a web page in the page itself. After I have everything working I will move it into an external .js file. It still sounds like a caching issue for your problem. How are you loading the external .js file from the master page?