You could try one of the other disks on the list and see if you have better results.
AVG usually has good results, or try this one: Avira AntiVir Rescue System - Download
The Avira AntiVir Rescue System a linux-based application that allows accessing computers that cannot be booted anymore. Thus it is possible to repair a damaged system, to rescue data or to scan the system for virus infections. Just double-click on the rescue system package to burn it to a CD/DVD. You can then use this CD/DVD to boot your computer. The Avira AntiVir Rescue System is updated several times a day so that the most recent security updates are always available.
If none of the boot disks work, then as gregrocker stated, try doing a repair install.
If that fails, you may just want to consider doing a complete reinstall.