Do you have Service Pack 1 installed?
As Maguscreed says, a clean install may be preferable.
But, on the repair install, can you get this far, from the repair install tutorial?
Right click on the DVD drive
Click on open
Right click on the setup.exe file, and click on Properties
Click on the Compatibility tab
Check the box “Run this program in compatibility mode for”
Select Windows Vista (Service Pack 2) from the drop down menu, and click on OK.