Hi,
First you might backup the necessary data on your current harddisk, then reformat the entire HDD and recreate the partitions. Try installing Windows Vista OS again. If the problem persists, the issue is most likely caused by the following two reasons.
1. The DVD drive might be damaged; have a test on another computer to check whether the Windows Vista Setup CD does work.
2. The disk may be defective so take it back to where you got it from and ask for a new one, also check for any marks on the disk and wipe it down with a soft, lint-free cotton cloth.
If you purchased the Windows Vista from Microsoft, you might directly contact our Microsoft Customer Service 800-590-9400/(800) 936-5700, who are experts in issues such as: replacement manuals, disks, service releases and service packs, product orders, policies related to copying software on additional computers, licensing, and product registration. I think that they would be much more helpful.
Hope the above information helpful !