Picture blanks out when there's a lot of ...

My Sony has a problem with screens that are mostly white (such as the Wii eMail menu, or commercials that start all white).  It's quite bizzar but when thre is a lot of white the screen blacks out momentarily then cycles back on.  It doesn't always cycle out for the same time but average recover is <2 seconds.  The lamp is not going off as when it goes black there's still the screen glow.  

toshiba 42hp66 screen blacks out for 1 sec then picture returns. occurs on all channels. switched the inputs, no help  thanks