if I type
I am getting an error as
notepad is not recognized as internal or external command
What is wrong here?
Check how you path is defined.
E.g. start cmd.exe, then type
If it is not in your path then add it. You can do this in several ways; the easiest is way probably via [My computer] right click [Properties] advanced system settings, tab [advanced], button [Environment variables]
Note that %windir%\system32\ is in the path by default. In order not to have it someone either removed it, or you or an installer set a new path replacing the old path. (Probably when you wanted to append to the path).