I have a computer that will boot (I think) but it requires an admin password to even allow it to boot. The screen is black and there is nothing on it but
Supervisor Password:
Is there anyway of changing this without knowing what the previous password is?
Yes, but it depends... How old is it? Desktop or laptop? "Brand name" or generic?
In most cases, you need to erase the contents of thebattery-backed CMOS RAM. This is done by moving a jumper, usually the one closest to the coin-cell battery. For example, if it were a two-year-old generic desktop PC, and you could find the brand and model of the motherboard, you could go to the manufacturer's web site and download the manual (usually in PDF form). You could then find the exact location of said jumper from the manual.
If the unit is newer or a laptop it gets trickier. Some laptops and newer desktops use flash memory (semi-permanent, not battery-backed) and require a back door or special techniques to erase or reset the password. Since this varies from brand to brand, we would need to know more.