Does your laptop have a recovery partition on the hard drive that you can access to reformat? If not,your best bet is to contact Acer with all the details of your laptop and ask whether they can supply you with a replacement back-up CD.
You may not see it as The Kestrel describes. Try Start>Control Panel>Administrative Tools>Computer Management. Then select Disk Management from the left hand pane. Normally Acer split their hard drives roughly into two. Post back with the size of each drive and let us know if you can see a third partition which might be 5-10 GB.