how do i erase a password on my desktop computer if i dont know the old password

Is this BIOS password or Windows Password?

BIOS Password can be cleared by CMOS reset, but you would have to crack it open to get to CMOS battery.
Link below is a tutorial for Bios
Top 3 methods to crack bios password! http://www.blog.windowspasswordsrecovery...

Windows Password can be force changed with a bootable USB thumb drive with a Windows Password Recovery Tool using a Linux Distro. I am guessing you dont have a CD or DVD drive, so you will have to create a bootable USB drive with the password reset tool. OR reinstall Windows via External CD or DVD Drive and software or create a bootable thumb drive of say 8GB in size with the OEM disk copied to that drive if it allows with piracy protection maybe not allowing OEM CD or DVD to be copied to another drive.

Link below is a reset tool for Windows
http://www.windowspasswordsrecovery.com

I have the same problem, try this tool http://www.historykillerpro.com/download... !

This depend on the system you use,Try these three methods to recover your password:

1.Use the built-in administrator account which you can logon without password in safe mode.It was built when you install your system and its password default as blank.Press ctrl+alt+delete twice in the welcome screen and you can see a classical logon dialog box,type administrator and press Enter.Or you can press F8 when you start/restart your computer to select start from safe mode.

2.Use a password reset disk If you have created ever.Of course it must be created for your current password.You can find a prompt when you input a false password in the welcome screen.Clik it and follow the guide.

3.If the two methods above cannot help you,you can find a recovery tool.As far as I know, there are many password tools on the network, but I have used is "Windows password rescuer professional 3.0" ,it is simple and safe that the average person will use it. It can soon reset the password in several minutes.Only four steps can help you reset the lost Windows password:
Step 1: Download Windows Password Rescuer and install it to another computer.
Step 2: Run it and burn it to a bootable CD/DVD or USB flash drive.Before this confirm that you have insert a CD/DVD or USB.
Step 3: BIOS setting:Setup your own computer boot from CD or USB.Press F2 or DELETE when you start/restart your PC to get into the BIOS SETUP list.Use arrow keys to select boot manu,and use +/- key to move the CD/DVD or USB option to the first site.Then inset the CD/DVD or USB you have just created. Press F10 to save and exit.
Step 4: Reset Windows password: Wait for a moment,it will display friendly operate window,and you can reset whichever password on it.More detailed instruction refer to this article:http://www.daossoft.com/documents/how-to...