Hi,

today I tried to reinstall Oblivion, but I was not able. My setup said that the data3.cab is broken and cannot use. So my system stop the installation and I am not able to play/install.

Can someone help me?

Usually means the DVD is scratched or dirty so can not be read properly -- look closely at the DVD and if you see dirt or oily fingerprints try cleaning it - if there are scratches on the surface you might be able to remove them by taking the DVD to a video rental place and having them resurface the disk for a small fee - if they are big or deep scratches you might have to rebuy the game !