If windows will not boot.
Power computer on. Hold Alt and keep pressing F10 at the Acer logo. You may need a password. If you have used Erecovery before you would have been asked to create a password.
If your first Erecovery the default password is 000000
If that doesn't work, do you have access to another machine to download and burn an Installation disk? http://forum.notebookreview.com/windows-os-software/604...
Burn it to a disk. Then either clean install it to your laptop by formatting the HDD, or create a partition to install it to. The 2nd option retains any stored data on the drive, you should then remove the old version of windows. You would then need to install all drivers from your laptop manufacturer's website. Windows would need to be re-activated using the key on the base of your laptop.