I am the admin

If you have wondered how people suddenly can't logon in guest, there accound, administratior. In most cases is is a hacker. To do this:

Get access to the computer .
At the log in screen press CTRL+ALT+DEL twice or start in safe mode.
Type administrator ,then press enter or in safe mode click on it.
Click start.
Click run.
Type 'cmd' without quotes.
Press enter.
Type net user.
Type net user administrator passwordhere. Where it says password here put the pass word you wan't to Change it to.
Press enter.
Repeat steps 9&10 using all the user accounts you saw when you did step 8.
Logoff and get out!