If two separate OS CDs are causing problems then it could be your hard disk. You can tell for sure by downloading the hard disk diagnostic utility from the hard disk manufacturer. Since you reformatted already you can use the utility to do a low level format (actually it just writes it completely full of zeroes) and then do a very thorough surface scan of the hard disk. The surface scan can tell you for sure if there is any problem with the hard disk. If the hard disk passes the manufacturer's diagnostic test then something else is wrong. All the major manufacturers (Maxtor, Seagate, WD) have these utilities on their web sites.