If you press F8 during startup of your pc, enter safe mode on your computer. Once safe mode has logged you in, click on your start menu and right click on my computer then click manage. Click on the button that has Local Users and Groups on it. In the Users container your user will be in there. Right click and click on "Set Password"
WARNING!!!! If you do this and you have encrypted ANYTHING on your hard drive, then you are going to lose it.
Hope this solves your problem
Regards
Phalebus