The more you do with your computer at this point (download updates, install drivers and/or software), the less likely data recovery becomes.

Search Google for data recovery software. You may need to remove your harddrive, put it in a USB enclosure (probably will need to buy one, unless you have one laying around or that you can borrow), then buy/borrow another harddrive, install Windows on there, then install the data recovery software, plug in the USB enclosure and follow directions for the data recovery software to see if you can get your data off the 'old' harddrive. If this doesn't work, and the data is really important, you can look into data recovery companies like Drive savers or so.

After you get your data (or not), use the USB enclosure to back up your important data for future situations where you need to reformat your harddrive or if you have the bad luck of your harddrive dying.