Re: HELP ME no administrator login
It's not dangerous to use IE (well, not with Mambo anyway, other sites might install spyware/adware without you knowing, but that is another topic), it's just that IE can be funny about caching sometimes. One suggestion is just to try it with a different browser if you have one handy.
I can't think of any reason why your backend login would suddenly stop working. What components did you install the last time you were logged in, maybe that will help track it down.