Since you didn't bother to write down the key or save the original email:
1) Go to http://www.bandicam.com/buy/ and scroll down to License check.
2) Input your e-mail and submit.
3) Go to your e-mail and copy the key.
You're running an outdated version of Bandicam that doesn't support NVENC on post 352.86 drivers.- Bandicam version: 2.0.2.655