The "DOS prompt" at Programs|Accessories may not do you a lot of good. It allows you to use command line functions, but it doesn't turn off Windows, and a file that's open and running in the "Windows Interface" still can't be deleted, even if you're using the "Command Interface" to try to do it.

You can use that window (it's actually called the "Command Window" since bronze became more popular than stone) to type msconfig, hit enter, and click on "Safe Boot" so that the next time your computer is restarted it will start without opening anything except "essential services" (i.e. in Safe Mode) where you're more likely to be able to delete something that Norton couldn't delete.

MSCONFIG has several tabs, and you can "configure" how the computer will start up at the next restart by "deselecting" individual things so that just those things are omitted during the next start.

My Vista Help file, searching for "Safe Boot," does - after poking around a bit - claim that F8 should work to get a Safe Boot, but says that a better search term is "Advanced Startup." This is because Vista designers believed in never using the same names for things as people have known for the last five decades, on the apparent theory that those are "old and scare people."

For the F8 (or whatever key your computer builder thought was better) to work, the key has to be pressed before the Windows Logo appears and must be held down until the Startup options screen appears. If you see a "Windows" logo, or "Windows is Starting," or "Starting Windows," you'll have to let it finish starting, then restart and try again.

John