to be perfectly honest with you, if there are software like FolderLock already available, then I don't see any reason why would you want to create one yourself unless the reason is purely related to learning. There can be several security level issues as well with such an application I would imagine and as Christian pointed out most such software are written in C++ which gives more control over the environment than C#.
Having said that, see if you pick up something from here:
LOCK-UNLOCK-C#[
^]
Cheers...