I can't disable caps lock with caps lock, shift or ctrl. I can only disable it with on screen keyboard. But when caps locks is off i can turn it on with the caps lock key. I am using xp.
I suggest to reinstall the keyboard driver if it is a laptop. If it still fails, you can check the possibility of a virus that blocks proper keyboard usage. Run a virus check.
I also had a problem, just do not remember exactly which keys! I tried to fix the problem myself, on my computer! Thought that the case in one program, but it turned out that my keyboard is broken, what is broken inside.