Did you create the backup discs?Do they include your personal data? If yes, try to follow steps from anonymous1.
If not...
Computers do not come with Restore disks anymore. The recovery information is stored in the hard disk in a hidden partition (about 12GB) and people are supposed to create the discs right after buying a computer. A practice that nobody does.
So you need to put the original hard drive back into the computer. Turn the computer on and hit F11 (I think) to bring up the recovery screen. There might be an option to create the restore discs. Another way is go in Windows/Start and there is a folder Gateway (or Acer) Management where inside there is a utility for you to create the discs. Once the discs are created (maybe 4...