Causes:
The repair option should be on the same screen as the Parition list. But, if the install CD does not match the installed version, you will only get the install option, even if its XP Home versus XP Pro. When setup sees OEM, retail and volume CDs installed, it does not offer the repair option. And also there won't be a repair option if the system hive is missing or damaged
Solution:
There are two methods you can do to fix the problem:
1. If you don't mind to have a new OS installation (all data will be gone), it would be better to reinstall your os.
2. You can also install a new operating system on the same partition by choosing another directory. If, during the installation, it asks to format or leave the current file system intact, choose intact. Once the installation completes, you can copy all your files and other info from \windows to your new directory. In this way, you won't lose any data on your old system.
3. Try to select the Setup option and then select Repair to repair your operating system. This option is just to reinstall os over the existing os and try to fix the problems. No data will be lost in this attempt.
Tips:
Maybe you can try to copy the CD, altering the data in the setup.ini file to "create" a disk of the right type.
