It happens on some computers; the lithium battery that regulates the 'real time' on your computer (any computer) can fail.
So, in the bottom right hand corner you may see the time; it may seem 'off', and if you hover your cursor/mouse over it, it may show a date that is AGES AGO!
THAT can prevent you from posting, or allowing things to show up.
Just a suggestion. Even if the battery that regulates the time fails, you can hover over the time and do the: Change date and time settings
I've had that happen to me, and it was so obvious, I missed it. So, when I find there's some odd anomoly, I hover over the date and sure enough, it will hiccup periodically and I'll see:
December 31, 2006. I just change it, and presto! it works. Good luck red dot.