db2pd: Database mydb not activated on partition 0
db2pd requires Administrator authority on Windows, in the command shell you are executing it.  Setting your ID as a member of the Administrators group on the local machine is not sufficient.

IBM adds "DB2 Command Window - Administrator" in your Start Menu to give you a DB2 Command Window that has administrator privileges (which is the recommended method).  Alternatively if you are using a normal command window (cmd.exe), you would have to start it by right clicking "Command Prompt" and choosing "Run as Administrator".

It might be possible to use runas to execute db2pd, but it's probably easier to just start the command window directly with administrator privileges.