Hey @ferwatch01!
I'm not entirely sure that this is the problem, but one thing that could be the problem is the CMOS battery being dead. The CMOS is a small coin cell battery (Usually CR2032) that is on the motherboard of most computers, and it allows the internal clock to keep running and BIOS settings to be maintained when the main battery is dead and the system is unplugged. Depending on the computer, a dead one could stop the machine from booting, or simply cause it to complain quite a lot about the date and time not being set. These can often die every few years, so a machine that has been in storage for a while could certainly have a dead one. The process for replacing it varies from machine to machine, but I'd start by taking off the small access door on the back of the machine. Look for a battery that looks like [link|https://valkyrie.cdn.ifixit.com/media/2021/05/01143522/AirTags_55-1600x900.jpg|this] (ignore the devices in the corners of the image). If it isn't under the access door, you may have to remove the entire back of the computer to access it. Again, this varies from machine to machine, but try removing all visible screws on the back and then prying the back cover off. Generally, these are held on by plastic clips, but if you feel a ton of resistance, try going to the location of the resistance and see if you missed a screw. Once you replace that battery, let me know if it works or not. If not, we can try a few other things.
Good luck!