really odd behavior- password not working

My sister (a notorious breaker-of-computers) came downstairs this morning and said her computer wouldn't log in. Knowing her to forget things all the time, I asked her if she knew the password, and she says yes. She pointed to her password hint under the prompt, and it is abundantly clear what her password is. I tried out all the variations it could possibly be, caps, not caps, full year, last 2 digits... EVERYTHING. She didn't forget her password, it just didn't work.

I've tried resetting the password with trinity rescue kit, and it said it was successful- 3 times- and each time I tried to log in it wouldn't let me in. I can't get to a command line, it just has me stuck at the login screen not able to do anything. I booted in safe mode with command prompt, and it brought up the login screen like I didn't click anything at all. I'm getting super frustrated. She expects me to fix this. I don't want to have to reinstall windows, I really really don't. At this point I've tried almost everything I can think of, and I haven't gotten anywhere. I'm worried that if I keep messing around with it, it just won't boot at all and she'll lose her pictures and files... and it will of course be my fault.

My question is: Could this be a virus? Is there one out there now that has been known for this behavior? I know she knows her password, since I've even logged in as her on a couple of occasions to help her fix things, and I used that password to log in successfully. Is there anything I can do short of reinstalling her operating system? Am I in over my head? Should I pay a professional to get it working? (preferably not, since that's expensive, but I'll do what I have to to make it work)

What do I do? Is there any way to pull her files off without logging in? I tried using an ubuntu live cd, but it wouldn't let me mount any of the internal drives, let alone an external one to move it to. If you think it's a good idea, I'll try downloading another live cd to see if that one works...

I hate being known as the techie. People automatically think I can fix things even though I'm no better at it than they are. Then they get mad if you can't fix it because they think you didn't try hard enough or something. Gah.

Thank you all for at least reading this far.
Anna

To pull files off with a Live CD I'd recommend Slax, I used it several times without problems so far.

Has this ever been resolved?

I'm having the same problem. I can't log in to Windows 7 on my laptop. I've tried every password combination I use for any of my accounts. Oddly enough I can swipe my finger on my UPEK biometric scanner and that logs me in just fine. Though login doesn't seem to recognize my password it accepted it as the old password when I went to change my password. Upon changing my password I logged out and tried to log back in and the new password did not work.

EDIT:
This actually seems to be more complicated then windows forgetting my password. I happened to think I didn't try removing the password and the remaking it. Removing the password went smoothly and the new password appeared to work. However I noticed some particular behavior. When at the login screen when I hold shift for particular characters in my password they don't show as though they were input. Shift works for 2 characters but not 2 other characters. This also happens at the switch user login screen. However when I lock the computer and login from that screen it works just fine. My keyboard seems to be functioning fine as I can type all the characters caps and lowercase, etc, etc.

Is there something broke with initial login and switch user login? Or is it just my machine?

Check that the keyboard layout is correct - as someone who remotes in to other systems a lot, I can't tell you how many times I've set the wrong layout in the wrong places!

The layout is correct. It's your standard US keyboard layout.

I was about to reformat my system. We'll see if this issue occurs on a fresh install of Windows.

If it's a desktop, try swapping out the keyboard for another, or just test that kb on another computer, anything you can plug into. If it's a notebook, do you have a kb around that you can plug in, and try again? It's possible the kb is bad, moisture can cause keys to actively input, but usually you can see this happen. Sometimes a kb will input random characters also. Worth testing.

Sorry I haven't posted back in some time.

I believe I figured out the problem, at least with my particular PC. I was in my BIOS messing with something and realized my NumLock key was set to enable the number keypad on the keyboard (keep in mind this is a laptop, without room for the keypad to be separate). I forgot I had changed this previously so I didn't have to hold the Fn key the whole time I was using the keypad. And the default setting in the BIOS is to have the NumLock key turned on when booted, so thus, when I try to login and am typing my password whenever I try to type any letters in my password that are where the keypad is, it's going to type numbers rather than the letters.

Nice troubleshooting. Hopefully that's the permanent fix. And welcome to Seven Forums.