A dying CMOS battery can produce the error you're seeing.  I would suggest changing it (it's a CR-2032 lithium battery). There is a password-clear jumper on the mainboard you can use to clear any errant password. page 63 of this pdf [URL]  
I bought this computer brand new from Dell and have never set any password in my Bios. But since I upgraded to Windows 7,  every time I boot I have to press F1 to bypass a message looking for a floppy drive.  My computer has no floppy.  Apparently the Windows 7 installation set a floppy drive as the default boot device.  When I tried to change the default in the BIOS I was asked for a password.  I tried a blank password, also DELL, admin and administrator - nothing worked. How do I discover the administrator password that was apparently set by Dell when I bought the computer so I can make my Hard Drive my default boot device? Mike P.S.   It occurs to me that it is possible that a floppy was always the default but that XP automatically bypassed the floppy if it found no diskette (or drive).   If anyone can tell me how to get Windows 7 to automatically bypass the missing drive, that would be a useful workaround.
What is Bios Admin Password for XPS/Dimension 400/9150?