If you acquire a copy of whichever retail, as opposed to OEM, Windows version – presumably in this case Windows 7 Home Premium, and probably 64-bit – you can reinstall using that.
Then, install the correct drivers for your model. If you also made the drivers and apps disc, run that; if not download them from the Acer Support site for your model.
Probably most people would think this is advocating piracy, but it is the key that matters, not the media. There is nothing untoward about downloading an unadulterated copy of Windows that requires a key to work properly and using your own key to activate it! If it was the wrong key for the media, it wouldn't be accepted.
The key on the bottom of the laptop will work, though a handy tip is while the original installation is still running, to find the key currently in use (the one Acer use when they install Windows at the factory, and which doesn't need activating Belarc Advisor will do this. If one of the keys – either the factory installation key or the one on the bottom of the laptop – doesn't work, the other one will.
You can find the copy of Windows at torrent sites, the trick being to identify the copy you require at the MSDN download portal, where they give the hashes, then Google the SHA1 hash to find the claimed unaltered torrent and compare it once downloaded.
If it matches, it's just as it came from Microsoft and safe to burn to DVD and install. A freeware called HashTab is an excellent easy-to-use tool for doing the comparison with.