you can do better - download a linux os! right now mint linux is very popular, followed by ubuntu. fedora and puppy are good too.
with linux you don't need the hassle of keys and !@#$. the os is very powerful and you can update the os very easily. if you want to run windows you can use a vm software or something like wine!
as for your problem, contact microsoft or acer with your problem . look around in your laptop, it might have the key printed on it. or look in the laptop manual.
do not ask for serials or keys here.