Unsupported Resolution - Blank Screen Unable to Change

Hey there, I know this is a windows 7 forum, But its one of the only places Ive found with quick and knowledgable answers to problems, so here goes.

I'm running Windows XP on a Desktop I just got as a gift from my brother, it was a project of his he gave up, but Im unsure of the motherboard its running, I do know its running 512MB of DDR ram, and at the moment is using the onboard graphics. I accidentally set it to 1920x1080 and now no matter what i hook it up to it will not display, I can see the boot menus and such but once it goes past boot it goes into "Not Suppot!" on my full HD tv, and "Unsupported Video" on my Samsung Monitor, and "Cannot Display Resolution" on my Dell moniter.

Ive tired booting in safe mode and in VGA mode but for some reason wont boot

So I need to know if there is any other way i can reset the screen resolution? Any Help would be amazing, thank you.

since it is desktop you try auto adjustment option in your monitor...

I have an ATI graphics card sitting here and a newer Matrox one i can pull out of a build in progress im not sure the specs on them but i can get numbers off of them (new to the whole computer building thing, my brother gave me a couple of his projects he didnt have time to finish)


EDIT - Put the ATI in there but no response when i moved VGA Cable to the card not sure if i missed something

Alright when i get home ill give that a shot, Im assuming i should try the older graphics card considering the computer itself is a little on the old side

I disabled it in the BIOS and switched the VGA to the Graphics card, got No Signal still,