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As me just saying eluded to, we will need more information.
To expand on Galactic Zoo's statement, if you didn't download it from the Google's Play Store there are any number of reasons the app isn't working for you. Just to name a couple, it could be a bogus app, it may not be compatible with your device.
I think I'm safe saying most around here would recommend only getting apps from Google, Amazon and your manufacturer's app store. Internet app stores are fair game for every sleazy sneezy app developer and you never know what you're going to get.