Perhaps it is on a hidden share on your HD? Boot up with bootmenu enabled, or change first boot in the BIOS...
If your computer is fairly new (came with Windows 7), you already have a way to reinstall w/o needing a disc. Consult your owner's manual for details. It should be clearly stated in the manual how to do this.
Usually, you'll press & hold a key (mine is F11) at startup. The reinstall wizard will kick in, it should ask you if you want to back up. If yes, then do so. If not, continue to follow the prompts, it'll format your drive, and when finished, it'll be as the day it was bought new. The process can take some time, depending on the size of your drive. You don't have to babysit it while installing, it'll stop where you'll have to make further selections.
There will be "crapware" that you may want to remove, such as trial AV's (Norton is commonly installed). Make sure that you don't delete anything that you may want to keep. Revo Uninstaller Pro (a 30 day trial) is good for this. You'll have the option to register the computer (just as if it were new), you can skip this.
Afterwards, you'll want to fully update your freshly installed OS, and reinstall any programs that you want. Usually the OEM has an updater installed (for your hardware), make sure that you update your hardware through the OEM, as Windows hardware updates can be older ones, and can cause conflicts/problems.
Hopefully, my post is of some help to you, while many prefers a totally clean install, I prefer this method, as your OEM drivers will be there, as I mentioned previously, you can update them, once you've reinstalled the OS.
Afterwards, check out our Free Software Database, look for Macrium Reflect Free, and you'll have a backup program, this way, should you need to reinstall, you won't lose so much data. Plus, it's a good practice to backup, for obvious reasons. You don't need anything fancy, a used (or new) drive installed in a case will work fine, connect it through your USB or eSATA (preferred if you have it) ports.
Best of Luck,
Cat