She is NORMAL.... ALL BABIES do this. It is age appropriate and developmental based. They are exploring... they get frustrated. They are human. They are going through a phase. The phase will pass. Then other phases will occur, all throughout childhood.
Remember, babies & toddlers do NOT have FULL "impulse control." So, they will not listen nor stop like a trained soldier. They can't, they don't have impulse control nor the cognitive development to do things at-will completely, nor the ability to just stop, period.
As a parent, you will feel like you are repeating and repeating things all the time, but that is how it is.
Instead of "no"... why not just redirect her? Or distract her? At this age, using wordy "explanations" about things is not age appropriate... because ALSO their attentions spans won't exactly follow every single little detail after 20 words of explaining.
1 or 2 step requests or instructions are best. "Sally, danger, stop." kind of things.
AND, have LOTS of things that she CAN explore and open/close and play with.. have a cabinet just for her that she can explore...put pots and pans in it, why not? Let her. Let her open drawers (that you have designated just for her).... let her have an old TV remote to play with and push the buttons.
For us, we never really fenced up anything... but we childproofed the cupboards that have chemicals in it, or sharp objects or important files/papers in them. Other than that... our kids were "able" to just cruise around and open/close things and explore. We let them. ONLY if it was a danger did we then pick them up, put them down elsewhere and then redirected them to some other kind of activity.
As for the entertainment center... well babies/young children love these... it is cool and has lights and buttons. Its only normal they want to touch it. MAYBE you just have to relocate it, put it up on a HIGHER shelf or cabinet or armoire or something... until she gets older. Or, you let her touch it and teach her how.... our kids would touch ours too... but overtime, we just taught them HOW to touch certain things ('carefully', 'gently') etc., and how NOT to "bang" it and "how" to treat it. That's what we did, and then by the time my kids were 2-2.5 years old, they could even load their DVD's into the player themselves and turn it on. Then the phase passes as they get desensitized to the entertainment center.
The "trick" is to 'teach' the child how to do things... instead of just saying "no" to everything.
ALSO, when you/Hubby are touching say the entertainment center... try talking OUT LOUD to yourselves (kids learn that way too) and say something like "Hmmm, I want to turn it on, but I need to be careful... I don't want to break it....its special. I will push the button softly..." and then do it, and talk it out to yourself, out loud, as you do things... that way, indirectly, you are "showing" your child what and HOW to do things. GRADUALLY, they will absorb it and learn this way too.
Saying "no" all the time... well a baby/child gets desensitized from hearing it all the time. So, simply use other words. Just say 'danger", or "stop" or "not now" or ", you will get hurt." And then you can actually SHOW her what can happen if she gets hurt or plays with certain things... actually pantomime it out and show her.
Also, you can teach her functional words... like: danger, hot/cold, on/off, fall down, owie, sad, happy, frustrated, gentle, soft, fragile, sharp/pokey, please, thank you, more, hungry, drink, etc. That way, she will actually build up a way to communicate with you and you with her.
The thing is, it will continue. That is what a child is. They are not a soldier. They will continue to explore and when they are having so much fun... sure, they don't want to stop. It does not mean they are "aggressive." They are simply frustrated.
MANY ways to circumvent it and teach a child. But it won't happen over night. It is ALSO a matter of the child getting used to the habits and routines of their parents...and seeing them and what they do and not do.
And to a certain point, you NEED to let her and "allow" her to touch things... and to let her explore...so that it (the object) becomes more common and not so enticing.
All the best,
Susan