Since you posted in the free hosting area I'll assume that it is indeed what you have.
Free hosting servers don't have the same uptime that paid servers do. If you want your website to be up all the time, you need to pay for it. Pay attention to the announcements, often there will be information about why a certain server is down. You can also check
this site to check on server status. It's not right 100% of the time though...so don't be alarmed if the data on the site is wrong. It should fix itself soon.