|On a desktop removing the battery or moving the jumper (on some models) will work. You can also use a boot disk with a debug routine do reset the bios....providing the computer will boot to A: or cdrom.|
On a laptop the bios are in an eprom, a small chip. The information in it will be stored for years without power.
If a laptop ,either contact Dell. ......the previous owner.... short the eprom....or use the hash.. 5 letters displayed after 3 wrong passwords to generate the master password or you can compare the make and model number and the service tag # to generate dells back door.
The above paragraph is in a gray area here so i will leave it at that.