to kill a process from taskmanager from command-line

First you should check that process is really found at taskmanager. You can list processes with command TASKLIST. To kill a process use TASKKILL.
E.g. c:\>tasklist
To kill a process if you know it's process id (PID)
E.g. c:\>taskkill /pid 12345
To kill a process if you only know it's name
E.g. c:\>taskkill /im "winamp.exe"
To find a process if you know partial name
E.g. c:\>tasklist /fi "imagename eq win*"
For more examples
E.g. c:\>tasklist /?
E.g. c:\>taskkill /?