1. Firstly, open Notepad and enter:
@echo off
:A
Cls
echo MESSENGER
set /p n=User:
set /p m=Message:
net send %n% %m%
Pause
Goto A

2. Now save this as 'Messenger.bat'.

3. Open the .bat file you saved, and CMD prompt should open up and you see:

MESSENGER
User:

4. After 'User' type the IP address of the computer you want to contact.
After that, you should see this:
Message:

5. Now type in the message you wish to send. Before you press 'Enter' it
should look like this:
MESSENGER
User: 27.196.391.193
Message: Hi
Now all you need to do is press 'Enter', and start chatting!

6. You might get an error that says:
"An error occurred while sending a message
The message alias could not be found on the network.
More help is available by typing NET HELPMSG 2273."

IF YOU GET THAT ERROR, DO STEPS 7-9

7. To fix this, go to START
Click CONTROL PANEL
Click on Administrative Tools(switch to classic view first)
Click on Services
Then find the 'messenger' service
Double-click to open it
You'll see Startup Type which would be disabled
Click on that and select 'Manual'
Now press the Start button and apply

8. Now do the exact same on the remote computer,
Because until this service is activated on that pc,
you won't be able to use this.

9. After you have fixed the error,Repeat steps 3-5

10. There you go, resume chatting!!

Thanks to Paisley-Techno-Kid