I upgraded to Ubuntu 16.04 2 or 3 months ago. Everything was running fine -- there were no issues. For the last few weeks I've been having these problems: (While using a browser) first Ubuntu will lag e.g. I will type something into an edit box and it will take several moments for the characters to appear. Immediately following this the tabs on the browser would turn gray, the mouse couldn't be moved and I had to shut the machine down with the power button. (It froze up.)
I say 'would' now because there has been some improvement. I took WinEunuuchs2Unix advice and installed the new Kernel 4.7.2. The whole issue of lagging and freezing seems to happening a bit less frequently now and the browser tabs aren't turning gray.
I installed Grub now (didn't even realize it wasn't installed.) I know I have to pick the last kernel before 16.04 upgrade. How do I do that?