Difficult task.
What you describe will not happen. But you can check with Dell support to see if the computer is registered to that owner. Then Dell will send someone out as an authorized service rep with a little disk that runs the fix... and has a cost.
I would first see if the hard drive can be accessed while installed in an external USB enclosure.
If it can, then even if passworded, you can put in a replacement drive. And Dell XP install disk will work.
Then you can buy a Dell motherboard on eBay. Many Optiplex boards are cheaper, and work better than the Dimension boards... for a cheaper price... around $70 to $85.... or refurbished Dell government computers are for sale at PCSurplusonline for $120 to $180 with shipping... just move the board into the 3100. And the dell OS will work.

 

Our official (and only) BIOS password support thread can be found here:
https://www.techspot.com/vb/topic109612.html

 

I have re-opened this thread, as the Dell Dimension 3100 is a Tower PC not a mobile laptop

You can either gain help on Dell here: https://www.techspot.com/vb/topic100658.html
Or just reset the CMOS jumper on the motherboard with the CMOS battery out
This normally removes BIOS passwords on PCs

 

I have already tried the battery out bit as well as the shorting of the CMOS battery jumpers - NBG (no b looody good) so will heave out the motherboard and short out the chips to see.
By the way, it is a desktop so not quite such hard and fiddly work as a laptop!

 

We don't find much difference between the Dell laptops and Dell desktop where password problems are concerned.

We have had excellent luck replacing the motherboards on the desktops... and many of the Optiplex boards are half the price of the Dimensions, and twice as good... though sometimes they don't fit the output locations if the cover plate is not included.
Be sure it is an official Dell board... most are still sealed in plastic... and it will run all the Dells OS install disks without a hitch.

 

It is not my intention to go chasing round looking for second hand motherboards to fit this heap. I hate Dell machines with a passion and it would give me enormous pleasure to recycle it - in other words jump up and down on it in my great big hobnail boots until it is dead.
As I think I said above, I have reset boards by shorting out chips before so I will try that - if it fails that is the end of it.

 

Hello all. Hopefully, my first post will be of hope. If you open the box up, you'll find a (usually green) jumper close to the power plug on the mobo. Remove the jumper, turn the computer on, watch monitor until it says something like, "password disabled," turn computer off, and replace the jumper. This has worked for me, literally, hundreds of times. Hope it helps you.

Take care,
Dave

"Newcomer, in training?" As a seasoned IT at a major university, I've learn that IT means "in training!"

Dave

 

Well done xedlgxe - that worked! Very many thanks for your input!