ANY SOLUTION TO A MAJOR OS PROBLEM?

I have made a real OS mistake that has made my laptop useless. The computer is a Dell Inspiron 1570. I installed Windows 7 Professional last night which went off without a hitch. When I rebooted, I got a message that my username and password were invalid and at that point it continuously recycles to that message when I press "OK". I have both the original "drivers" and "applications" disc but the laptop refuses to recognize either. I tried to reinstall but the same message keeps coming up. Should I delete or format the partition losing all my stuff? I simply don't have a clue. And, of course, I cannot find the system image disc I made. Suggestions? Thanks. uscbob2010