Can't play Day z!

[i'mfriendly! 0]

i have been trying to play dayz and i have been experiencing tons of difficulties. i have been playing since beginning of june no problems at all. first i cant respawn after a hacker takes control of my body shooting my friend and killing my guy then hiding my body.... i didn't even get a death message so when i try to come back on later i get stuck on the set-up completed please wait screen. i wait a day when i try to play again i get an error message file too short...... blah blah blah arma2oa expected some hex number and got this hex number. i uninstall then reinstall the game now it says the cd key isn't valid. i bought the game off steam so the cd key should be legit. i don't get why this is happening to me and something has to be done about it. i ran steam as administrator checked the file integrity of arma 2 and arma 2 oa, both had a missing file of some sort. i defragged the cache files and still nothing. im really frustrated and i really need some help. i don't know why this happened now all of a sudden