how to link the form so that it should display as soon as the computer gets started and the user should not access any other thing first he has to attempt the form then after successfully he can acess rest of the other option

the form will be containing user name and password i hope i'll be responded back as soon as possible

What's to stop the user from just closing the window? or clicking start or using a keyboard shortcut for windows explorer or run?

If you are interested in disabling all the above then you are not talking about a form, but a different shell. If I judge by this thread: http://www.daniweb.com/software-development/vbnet/threads/397492 that you've created something like this is totally out of your league (shell = windows desktop = explorer.exe so you need to change the way windows act on various events like windows logo + E ).

Why don't you describe what you want to do and perhaps we'll brainstorm an alternative?