Unable to Log-In to Windows

My system isn't "crashing" per se; but I'm having what might be an even more frustrating problem.

Somehow my Windows 7 user profile has become corrupted (I can't imagine how; it was working perfectly this morning). As the machine in question is a laptop, I have it set to require my password before opening the desktop. On system startup, it still boots to the login screen and still requests my password; but when I enter the password it says that it is unable to load the profile, automatically logs out, and takes me back to the login screen where I can repeat the cycle endlessly.

I should be able to simply wipe the harddrive and return to an earlier backup state; but there are some files I want to copy before doing so. However, because I can't access the desktop, I can't access the files.

Is there a way of reaching the desktop, if only to back up some files before wiping the system, without passing through the apparently impassable login screen?

One possibility (this happened to me after I added a KB combo) is that the keyboard is no longer the one in the system for some reason. At top left there's a dropdown button if you have more than one KB/language installed. Try changing (this didn't work for me). If this doesn't work, just imagine you are using a default US keyboard and see if that works (Y, Z, Q, M etc. move around in other KBs). Alternatively again, try the alternative input methods from the bottom left dropdown...
Afterwards, when you're in, make sure you create a new Administrator user with a password that does not involve keys that change places. Numbers are probably safest.