Did you happen to reinstall windows 7 without using recovery disks? With brand laptops, I wouldn't reccomend, especially since very few have access to a plan windows 7 DVD.
Its also possible a virus corrupted the partition. In the future, make sure to make recovery media for your laptop, saves ton of future hastle. All brands should have some sort of software installed that allows you to do this.
Assuming using the software to burn recovery media is no longer an option, you have the following options:
Option 1: You can order recovery disks here: http://store.acer.com/store?Action=eRecovery&Locale=en_US&SiteID=aceramer. This means that all proper drivers get preinstalled as well.
Option 2: Find someone who has a retail copy of Windows 7 (your version, aka Home Premium, Professional, 32 vs 64 bit) if its your only laptop. Install appropriate version, but you must go to support.acer.com and go through the process of downloading and installing drivers. Depending on driver support though, you may or may not get the proprietary button functionality back exactly the way it to use to be. You'll need a spare computer to get the wireless or LAN driver at minimum, then able to download the rest. Or gather them all at once from spare computer.
Option 3: If you have a spare computer, can download needed copy of windows 7 from here:
http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_install/cannot-find-digital-river-download-site/66a8439b-0d16-4b70-92f7-1c8486a46ebf
For Options 2 and 3, you'll have to go through the activation process for your windows product key, don't forget to do that!