Welcome to the forum.
Did you purchase from Adobe, or did you Register your copy of PrE 11 with Adobe?
If so, then your S/N will be on the Adobe Web site. You just need to log-in with your Adobe ID number, then go to your software page, where all of your purchased, or Registered software should be available to you.
Never mind. I found it.
General FYI... Windows "encrypts" program serial numbers when they are entered and saved to the hard drive for program activation
This is so someone who "wanders past" your computer will never be able to see your actual serial number and steal it