Q: Why can't I download OS X Yosemite from te appstore?

Thanks for the response.  This is a second hand unibody laptop.  It has an Intel C2D chip and 8GB of DDR3 RAM.  Since I can't access any info on this computer (other than the install assistant, which goes nowhere) I have no idea if any of the actions required before selling the laptop were taken by the former owner.  Since the Apple site is asking me security questions I never answered when the account was set up, I can't get past the edit screen for changing anything about my account so I can associate the laptop with the account.  I guess I'll have to set up another account.  As far as I understood, Apple OS X was associated with the machine serial number - which I can't get to as it's only available after an OS is installed (there's no serial number on the outside of the machine to the right of the legal info on the bottom).  All that's there is the model number (A1278).  I can't download or update anything from the appstore (at least as far as I can see) without the some form of OS X running.  You indicate the unit may need new firmware to run Yosemite.  If I have a download assistant showing for Yosemite, does it mean the laptop was running this version of the OS before it was formatted and sold?  If so, it was either purchased by the former owner or updated from a prior purchased version and should still be available for the unit.  Am I misunderstanding something here about how Apple manages their OS distros?  From the above you can see I'm in somewhat of a classic "Catch 22" situation here and could use some help.  If all else fails, I'll pop a Linux distro into this thing (which sort of defeats my attempt to get some knowledge of Apple systems to see how well they stack up to my MS/Windows world.  If that's the case, I've wasted a few hundred bucks and have another Linux laptop (all my Windows laptops are Intel i5 or higher and 8 to 16 GB RAM w/SSDs) and run Windows 10 Pro.  Most were second hand machines off lease and I've upgraded them to donate to students and schools in the area.  This one is more of a trial machine to see if Apple products will be part of the program.  Right now, I'm feeling I should maybe stick with the what I know best, but I've had a few kids that ask me about MacBooks and I'd like to help if I can.  Anyway, thanks for the help and advise.

THANKS!  Found it (funny place to put it, but it's there).  Now I at least know the serial number for this thing.  Didn't see this on the Apple Support site when I was looking for info on where the serial number would be listed - only saw the description of it being printed to the right of the legal info on the bottom of the case.

Thanks to all for the help and advise!  I have ordered a copy of Snow Leopard from Apple and will install it as soon as it arrives.  As I indicated, I was unaware of how Apple manages it's distros for operating systems and assumed it was something like MS uses.  I was pleasantly surprised to see that the cost of Snow Leopard was $19.99 - not the $80 - $180 MS would charge for a copy of Win 10 (the only one available from MS).  If the MacBook turns out to be more useful than the various ChromeBooks I've seen and used over the past few years, I just might scrap some of the MS based laptops I have and switch to a more modern MacBook.  Again, THANKS to all for the help.  I'll let you know once I have this little thing up and running.  I'm really curious to see how it handles the somewhat small 8 GB of DDR3 and a 256 GB SSD running on an Intel C2D 2.0 GHz proc.  I know MS OS's consume lots of resources and this combo would result in slow or logy performance.

Just started the update process without using this tip - man, am I sorry!  It's been running for the better part of 2 hours, with no indication it's doing anything.  It rebooted and all I have on the screen is a deep space picture with a colorful pink nebula in the middle.  Wish I knew if it was doing anything....  I'm on a fast  internet connection (30 MB per second) and this is as bad as dial-up!