TV flashing rapidly like a strobelight?

okay so for the past month my tv has been flashing like a strobelight after like an hour of it being on. it seems to activate whn the tv goes black. Ive tried seeing if it was my ps3.. my hdmi calbe.. its my tv for sure. But I have no idea whats causing it. Also my computer monitor shuts on and off on its own. it will go black for like 10 seconds, then reppear for 3 seconds, and do this endlessly. it used to only do it on some occassions and i would just shut it off and back on. now it dioes it no matter what.I dont know howe the *** this is happening to my electronics but it is sooo annoying as it prohibits me from doing almost anything. any ideas, please help!