You can't do a 'repair install' because you need to launch the Vista DVD from within Windows, not, as you have been doing, booting straight from the DVD; that is why the 'upgrade' is greyed out.
If you cannot launch Vista and none of the repair options will work a new install is the only other variant.
To save problems in future it is actually a good idea to make image of the hard drive, using something like True Image. What I do is install operating system, download all updates, check system I working okay for a day or two, activate system, then image the drive/partition. Any time I get a problem I can re-image the drive/partition quickly and be up and running without much inconvenience. And minor fixes are done by using any registry repair utility, there are plenty of them on the market today.