Lost Password

I restarted my computer earlier, and when I went to type in my password, it
wouldn't except it. I didn't change it, so I don't know what the problem is.

And since I can't log on to that computer, there's no way I can get programs
or anything. I don't have a CD thing that I've read about either.

That computer is Windows XP and nothing like this has every happened before.

Any advice what I can do?
.