Seems I keep posting stuff that slowly makes me lose all virtual friends here, making me the most unpopular member. Here we go again:
The only possible and acceptable solution to offer to the OP here is to do what Thorsen, Borg and Solarstarshines have told: Do a fresh, clean install, either with your own valid install media or ordering it from Acer.
I find all further methods and discussion about them totally irresponsible and both ethically and morally wrong. Even hinting the OP where to find relevant information is in my opinion disgusting, as this case involves personal information from previous owners of that computer. If cracked or passwords bypassed, the new owner could have access to banking, tax, social security, health, insurance, simply all kinds of protected personal data, as well as emails and such if the user had enabled "Remember me" / "Keep me signed in" or similar options. Not to speak about personal photos and documents such as diaries, letters, CV and so on, as well as sites like Facebook, Twitter, Google+ and such.
Nobody except the old owners has right to that information, any ethically thinking person would not even think other options than to clean install wiping the HDD empty.
Kari