Here is the procedure for a Gateway/E-Machines. But it should be very similar for your Acer:
1. Copy all your own files and folders to an external storage (Disc, USB stick even SD card - 1 GByte capacity should be ample - even 512 MB)
2. Shut the PC off
3. Turn the PC back on and keep hitting the F8 key repeatedly until the Advanced Boot Option Screen appears
4. Click "Repair Your Computer" –if you are not already on it, use the up and down arrows to maneuver to it and then press ENTER
5. Next you have to pick your country and click OK
6. On the "System Recovery Options Screen" click "Restore Application" (last option)
7. Follow the on-screen instructions
8. When prompted, click on "Full Factory Recovery"
9. Click "Next"
10. Click "Yes"
11. Go and have a cup of coffee - don't touch anything - for a while it seems like nothing is happening
12. After many minutes, recovery will complete and you click "Finish"