|Why are you trying to boot from the Vista CD/DVD? |
What is the problem you are trying to solve?
First open your PC and make sure all cables are fully pushed into their respective slots and memory devices are also firmly in their slots. Then try again.
Second can you go into safe mode? Hitting the F8 key as your PC boots up should result in you receiving the option screen which will allow you to select safe mode.
Report back with your findings.
☺ When everything else fails, read the instructions.