First thing to do is save your personal files. You can do that this way,
http://www.sevenforums.com/tutorials/93347-copy-paste-windows-recovery-console.html
Is the old Windows 7 DVD the same as yours, ie Windows 7 Home Premium, and is it SP1? I'm pretty sure an non SP1 DVD cannot do a startup repair on an OS with SP1 installed. If you don't have one, you can download official ISO downloads here
http://www.heidoc.net/joomla/technology-science/microsoft/14-windows-7-direct-download-links You want the Media Refresh, I'm pretty sure. Be sure and download the same version you have now or it will not activate or do the repair.
Try to use the one you have and boot through until you get to the options page where there are several options. Choose Command Prompt, type C and press enter, at the C:/ prompt type CD boot and press enter. at the C:/boot prompt type this and press enter after each one
bootrec /FixMbr
bootrec /FixBoot
bootrec /RebuildBcd
Then exit and try to boot.
If that does not work this is about everything that can be done in your situation, just use the newly downloaded ISO file, burned to a blank DVD or to a USB drive with
Windows 7 USB flash drive
If none of those worked, I think you have little choice but to do a Clean Install. Just get all of your drivers first if possible. I put them on a USB Flash drive, especially the Chipset and Lan or Wireless driver. You will have to be able to get on the internet. First install Microsoft Security Essentials (
Microsoft Security Essentials - Microsoft Windows)
Run all of the important and recommended updates except the Graphics card update. This will make the clean install work great, providing you have no hardware problems.
http://www.sevenforums.com/tutorials/1649-clean-install-windows-7-a.html