How to open pc asking for password which i do not

if it is asking for the BIOS password then you must open the PC and remove the button cell from the mother board for a minute or so and re insert it. This would remove all settings of the 8IOS.
To re set the PC BIOS you must press F2 at bootup and set all the settings again.
However, you should never use a password as one tends to forget it sooner or later.