If you have forgotten the password for your computer, and consequently cannot log in, the good news is that there's a simple way to regain access to your system which even a beginner should be able to pull off. There are now a series of "password reset" programs released onto the Internet, which have been designed to reset the stored password on your computer, allowing your PC to log you in without the need for a password.
The way to reset your pass is to use a software tool to look at all the stored password files & settings on your PC, and then remove them from your system. All Windows computers store passwords in the same way - by saving them in central files & folders on your hard drive. These settings allow your computer to basically "compare" your inputted password with the one on file, allowing it to quickly tell if you typed it correctly or not.
If you want to reset the password, you need to remove the stored settings from these password files, and the way to do that is to either use a password reset software tool, or to reinstall your Windows installation. Reinstalling Windows is an option for everyone, but is limited by the way it wipes your entire computer. This is a big problem for the people who use their computers regularly, and is not advised. The other option you have is to use a password reset tool, which will basically scan through your PC and remove the various password settings on your computer. This is a much more effective way to regain access to your computer, as password reset programs don't cause nay damage to your files / settings.