You need to restore your Windows 7 OS by booting your Acer from the Factory Recovery Discs which will also install all the necessary drivers.
If you didn't make a set of Recovery Discs when your Acer was working okay, or you didn't get a set of Recovery Discs with the laptop, you may be able to order a set from the Acer Store online.
For USA: https://store.acer.com/store?Action=DisplayDataValidationServicePage&Env=BASE&Locale=en_US&SiteID=acerna
For UK: No online ordering service available for Recovery Discs. You must contact Acer Support by phone on 0871-760-1000