Sims 3 Help

Hello,
i bought sims 3 the day it came out and installed it on my computer it worked fine and nothing waswrong, i then re-installed windows and tried to install Sims 3 again but it kept saying 'cyclic redundancy check' ive gone on all the wesbites and thought and tried all the possibilities to make it work but however t didn't. i tred it in my downstairs computer and the sims installed perfectly without any problems or messages, so i then went and bought a new external hard drive and tried to install Sims 3 on tht however the external hard drive does not detect any of the Sims games or anything high performance but is able to detect small disks. (my computer specifications are all above the minium aquiremtn for Sims 3 but still wont install on either CD Driver.

Summary: (Internal CD Drive) detects disk but canot install as it says 'cyclic redundancy check'.
(External CD Drive) does not even detect the disk at all.

thx n soz for making it so long, just thought it might help with the advice :)