Imac 27 settings changed

I DL & PP a lot of pictures mostly using Aperture3 & Lightroom3 .. Yesterday after doing some pictures I re-booted the comp and when it re-started I noticed the screensaver was different (I had it set to never come on) and it never went to sleep .. I changed the settings back but this morning I noticed no new emails (I use ISP email) and a box on the screen saying email info & password had to be re-installed ..I have noticed over the last week every so often the screen would give a flash sometimes 2 or 3 flashes ..

Any ideas what happened ..