Mom's been crying at least an hour each day, when I ask her why she says she doesn't know. Anyone else experienced this?

I agree that you can't make her happy. She may be anxious or frightened, so you can ask her what's bothering her. I'd validate her feelings, saying something like, "I know, Mom. Life is tough sometimes." Once you've validated her feelings you can try for distraction which may or may not work. Comfort her if you can, but don't let this rule your life. Continue working with her doctor.
Take care,
Carol

My MIL did the same thing for a couple of months, pretty consistently. She is also treated for depression and anxiety. MIL has vascular dementia, her other son said she would cry in a similar manner years ago when she had been drinking. It seems to me that she has a sad thought and just can't get past it. Almost as though her brain has lost the ability to move on to another thought. Nothing makes her feel better, no reassurance can stop the crying. The similarity between the drinking crying jags and her dementia crying jags seems to indicate impaired brain function is causing the problem.

She still does it occasionally these days, the current crying jags are quite brief. I think one reason they are shorter is due to MIL just not having the strength to maintain the crying these days.

my mother is completely emotionally dependant on those around her also, cries a lot, can be smiling the next minute. bipolar in my moms case. i dont think you can make a miserable elders life " happy " . distraction is about the only tool you have, reasoning will result in your brain melting down.