How can I login to my dads PC without knowing his password? [duplicate]

I used offline NT edit for the job. Its a single utility but it works like a charm to clear out passwords, add/remove users and so on. With this I was able to get my Win7 back. Also fully compatible with XP and Vista of course.

You could also try Ophcrack - It can look up the password for most windows systems and tell you what the old password was instead of changing it.

Did you try the car registration number or license plate #, both with caps and with lower case?

real simple... u just need KON-BOOT disk you can get cd-image from http://www.piotrbania.com/all/kon-boot/

it's a few KB download, burn it over any CD... then boot from CD as Primary Device a Kon-Boot screen will come; press enter and it will move onto starting Windows Vista...

when the normal log-in screen comes, just enter any fake password and it will accept...

this way you don't need to change/wipe original password and trick Vista to allow you log-in