Website is not coming up?

When I try to go to my website online it does not come up. 
For example www.mousetrips.com that does not work it brings up an error message saying the page can not be found. However if I type it in like this http://mousevacations.homestead.com/ it works. Whats the deal and how do I fix this? This is my business page and its important I get it back up and running. I have had this page for many years. Thank you