I'ts sort of the ussual problem when changing from HDMI to analog connection (no image /video output), but the difference is that it has been connected to an analog TV for a while..
I've tried solving it the ussual "hold till 1-3 beeps" solutio, but it still not working.
OK, have both cables hooked up when you are making this change. Go into setting on the PS3, and make the change to the appropriate video type (vga or HDMI), then change the INPUT of the TV to match the cable input for which you just made the change. Confirm you can see it so the PS3 will continue to use that method for video!