Fallout 3 for pc probs

Hello,
i have a dell inspiron530 dt com with 8400 gforce . fallout 3 works it just when i download the 2nd disc the computer windows explore wont respond and when i eventually get it downloaded the games addons wont play right theres just exclamation(!!!!!!) marks were the addons are in the game please b4 i smashhhhhh my computer