How to get unique computer info for licensing.

There is a famous software license manager claims that they can implement the following licensing process using their API:
1. Get the serial no. of the hard disk where the application installed.
2. Send silently the hard disk serial no. and registration information to licensing server to do some kind of encoding.
3. Return back the encoded information(may be the keys also) and store it under the application folder.
4. When your application being executed, the serial no. will be compared to that of the actual hard disk so that your application cannot be moved to another PC.

I want to implement the above by myself, however, how can I get the serial no. or other unique information that can represent a PC?  I am using c#, can anyone provide me some coding?

Thanks a lot.