Once you've booted to the DVD, then try the following:
· Do a Startup Repair by booting to the genuine Windows Vista Installation Disk (or one you can borrow from ANYONE) or from a Recovery Disk. Here's the procedure:
http://www.bleepingcomputer.com/tutorials/tutorial148.html. To boot to the CD you may need to change the BIOS to make the CD-drive first in the boot sequence. To do that, wait for the screen that tells you the F key to push to access the boot menu or boot setup. Push it quickly. Make the changes, save your work, and exit. Put the CD in the drive and reboot. When prompted, push any key to boot from the CD.
If you don't have either disk, you can make a bootable Recovery Disk using
http://neosmart.net/blog/2008/windows-vista-recovery-disc-download/ along with burning software like:
http://www.snapfiles.com/get/active-isoburner.html and, of course, a blank CD.
If that doesn't resolve the problem, try the following:
To run the Bootrec.exe tool, you must start Windows RE. To do this, follow these steps:
1. Put the Windows Vista installation disc in the disc drive, and then start the computer.
2. Press a key when you are prompted.
3. Select a language, a time, a currency, a keyboard or an input method, and then click Next.
4. Click Repair your computer.
5. Click the operating system that you want to repair, and then click Next.
6. In the System Recovery Options dialog box, click Command Prompt.
7. Type Bootrec.exe, and then press ENTER.
Note If rebuilding the BCD does not resolve the startup issue, you can export and delete the BCD, and then run this option again. By doing this, you make sure that the BCD is completely rebuilt. To do this, type the following commands at the Windows RE command prompt:
http://windows7.iyogi.com/support/windows-7-boot-manager-error/
· bcdedit /export C:\BCD_Backup
· c:
· cd boot
· attrib bcd -s -h -r
· ren c:\boot\bcd bcd.old
· bootrec /RebuildBcd
Good luck and I hope this helps!