Apple full size USB keyboard - ESC, tilde, tab, & caps lock not working

I was logging into my email account yesterday & went to tab from the username to password fields & the tab key is all of a sudden not working. It was working the day before, but not now. Upon further checking, the ESC, tilde, & caps lock buttons don't work either. So ESC, tilde, tab, & caps lock are all not working now. (???)

I have the white w/ clear base full size USB wired keyboard. When I unplug & plug back in the USB cord or shut down & restart, the light on the caps lock key does come on as it should.

I have tried many of the various fixes (Universal Access, etc) that I've found online, but to no avail.

No spills or damage & I can't imagine that they all 4 would work one day & then be too dirty to just not work the next.

Any ideas to resolve???