If you have downloaded it illegally than it wont play.
Bohemia Interactive have placed a code in it that detects whether or not the key being used is a factory key (or a keygen one) and if the game is running of a crack.
Most computers can run it fine its just a matter of tweaking the settings. alot of the default settings are still 2 much for basic
PC's so that is where you attention should be placed first.
The blur effect when you turned is something that pissed me off to no end. then Bohemia sent out a patch that allowed you to turn it off

.
Anyway thats my 2 cents on helping.
I was drawn to Arma after the original Flashpoint games which are still better (gameplay wise) ive been skinning and modding arma 1 & 2 for a while and in my experience there arnt to many people that stick with it due to the gameplay style.