How to fix a resetting Dreamcast, or a Dreamcast that cannot keep the correct time or settings
This is actually a pretty easy fix, Open up your Dreamcast (you can refer to one of my other guides if you need help on doing this) and near the front of the Dreamcast (Near where the controllers plug in) locate this.
Take some pliers and squeeze all the metal things in there and make sure the prongs sticking up are touching the metal lumps inside of there (You'll know what I mean when your actually looking at it, that picture was really just meant to locate it and you can't really tell).
Resetting Dreamcast Fixed!
To fix the Dreamcast that can't keep clock settings/other settings you will need to purchase something. Find this battery.
Simply take that battery out and replace it! Problem solved! Not all Dreamcasts have that blue plastic stuff around the battery. The one I decided to use for this guide did though. If yours has it there's really no problem in just ripping it off if you really need too.
As you can see, both parts are very close to each other.
Good Luck and happy gaming!