Early '09 MacBook (13") date & time reset itself to June,2000, nothing works!

[leef]

My early '09 MacBook (model A118) reset it's date and time to June,18, 2000, date and time pref. freeze up when I try to reset it. As a result, nothing works any more. Have tried many ways to reset, but it keeps reverting to 2000. (the month and date advance, but the year stays stuck in 2000) A millenium bug? Sure likes that year! So now, none of the programs, the browser (Firefox), Gmail, nothing works, I guess because they are all from 2016, and aren't recognized (?)
My brother (a Mac user for many, many yrs., tho' not a tech) and I have been trying all kinds of things we've come up with, from various books ( O Reilly/ Pogue says nil on this, that I can find) and the internet, nada!
Everything ran great before the change, one day, boom, she no work!
Any help any of you can suggest would be deeply appreciated, I love the Mac, and the OS (Yosemite 10.9.5)--lot's better than Windows/Dell backup I've been using.
Thanx in advance, Leef

 

[leef]

p.s.-Leef again-- forgot to say, an info window opens when I turn the MacBook on, says
"You're computer clock is set to a date before Jan. 1, 2008. This may cause some applications to behave erratically.
To reset, open date& time pref........" understatement!
That's all I've got !