Itunes will not download! help plz!?

i had itunes for my ipod touch but it started having problems so it told me reinstall it but when i tried to reinstall it says that im missing items and i need to modify??? im computer illiterate and i miss itunes! also my husband and his friend download something to sweep the computer whatever that means and my problems started then so im thinking something got deleted that i need... I tried to download off internet but it gave me the same warning.