Either Leave it blank or (assuming you are using Home) set an Admin Password (via safe mode.
1. Turn off your computer.
2.Power on and hit F8 just after the BIOS check is complete. Select Safe Mode from the List. Its around the top of the list.
3.On the next page press ENTER.
4.Work you way to the Desktop. Goto Control panel...by:
*Clicking on Start\settings\ControlPanel
5.Double Click on Users Accounts
6.Select the Administrators Account from the list.
7.Apply a password.
Then restart the system.