Here is another option: However, let me digress. as one of the previous commenters stated, "backup ALL your files" or better yet create a clone, or an image to re-install later. Ok. here is the problem I had and what I did to solve it. "Restore Toshiba Satellite L775D-S7135 to Original Windows 7 with created recovery disk set when holding 0 doesn't work and F12 boot selection doesn't work". Since the aforementioned did not work, I downloaded a free Win 7 Home Prem ISO and burned it to a DVD. I put it into the drive and executed the 'setup.exe' file. It took a while to install. THEN, when the option to enter the 'KEY' I skipped it. Re-booted laptop and THEN the F2, F9 & F12 keys worked so that I was able to insert my restore disk set (created when I first purchased it). I opted for the COMPLETE erase HDD and restore system to factory original. NOTE HERE!!!!! You MUST not have ANY USB cables connected; usb sticks, drives, mouse or any other EXTERNAL hardware. ONLY the AC cord should be plugged in. Worked for me. Good luck.
P.S. using diskpart may not be the best option because it interferes with the original system's configuration for the 'Recovery' partition/sectioning on your HDD.
just sayin.
As far as the 'KEY' goes, you can use your original; usually found on a sticker on the laptop along side the ser. num.