Why won't my fallout 3 run?

I downloaded fallout 3 from online. I used power iso to have my computer read the file as a disc so that I could install it. After I installed it I pressed play and it said an error had occured. I tried reloading it a few times and I even restarted the computer. After a couple more times i clicked on more info about the error and it said "This error report includes: information regarding the condition of Fallout3 when the problem occured; the operating system version and computer hardware in use; your digital project ID, which could be used to identify your license; and the Internet Protocol (IP) address of your computer." I have no idea what this means, if anybody has a clue on how to get the game to work, please answer.