So, you don't know whether the username or the password is causing the problem.
To check the username, do a
password reset.
You will see on that page there are two sets of instructions:
* I haven't upgraded to a Jagex account
* I've upgraded to a Jagex account
If you are still logging in with a username you will need the
I haven't upgraded to a Jagex account
set of instructions.
If you follow those instructions and get told there is no username login recognised, post back and I will refer you to another support page.