If all monitors do it, it's either the power at that location (did you check that by trying those PC's somewhere else or with a UPS?) or the PC. No other things are involved.
If it's the PC it's either hardware or software. The only way to prove that it's hardware is to prove that it isn't software. And the only way to do that is to restore to factory conditions.
We have two Dell desktop PCs running Windows7. Both run dual monitors. Within a few days of each other both systems monitors started randomly blinking. Not really turning off then back on, but more like a blink that goes to a blue screen then right back on. Annoying as all get out. Dell has replaced video cards x2 on one machine; mother board x1 on the same machine. We've swapped monitors with ones that are known to work to no avail. Now they want us to restore system to factory specs. No new programs were installed immediately prior to this starting. Anyone have any ideas what might be causing this. Dell is I think out of ideas and wanting to blame software. Really don't know where to go from here. Anyone have any ideas