Win 7 Log-on Problem Won't Go Away....

When I tried to log in to my Win 7 OS, my User Profile wouldn't accept my password...

When I tried to use my PW Reset Disc (on a USB stick), the procedure took me through creating a new
PW, but then when I tried to log on again, Win 7 wouldn't accept the new PW...

Then, using the "Offline NT Password & Registry Editor," password reset tool, I tried to retrieve/reset my PW, I wound up completely losing the whole User Profile Log-on Service!

This happened before in June, with the OS User Profile denying my regular PW at Log-on. That dilemma was fixed only through a torturous Registry copy-and edit session to create a new User Profile; no PW Reset Disc or PW Reset tool (program) was used in that session...

Now, as I work to fix this aggravation, I'd like to know WHY this Log-on PW denial happened AGAIN, and WHY it happened in the FIRST place!

(A command-prompt scan by an AV rescue program found no hard-drive errors, BTW).

I don't want to get hit with it a THIRD time!

Thanks in advance for any suggestions....