I don’t know your technical skills, but the short answer is creating a new administrator account and now you can change/reset password from your account. There is so many tools on the industry like a flash-drive to unlock your account, or the in the worst case, making a copy of your personal files and reinstalling windows.
Well, there is many of possibilities, not because is new it will work better, for example a computer of 3 Years ago with a core i7 processor will perform better that a brand new computer with a Celeron Processor. Also storage a SDD of 2 years ago will work faster than a brand new HDD 5400RPM. You need a geek talk to resolve all your questions.
Depends how gentle you are with the screen, most of the times you can remove the screen without see any extra damage, sometimes the crack just go a little bigger that you can not see it, and if you are not using the right tool and forcing too much , you can damage the glass and even damage the LCD Screen.
To be clear, because is a lot of confusion between microphone and speakers, microphones are a input device, if nobody can hear you is a microphone problem. Speakers are output devices, if you can’t hear is a speaker problem. Microphones in this model are attached to the motherboard with soldering balls, and you need a soldering equipment to do the job.