You need to make a distinction between "multi-region" and "multi-format": you don't always get both features in the same unit, and NEVER in any dvd/hdd recorder like the Sony 780. When you region hack a dvd player, odds are it will also automatically do a format conversion during playback, enabling you to watch the video on any random North American television. Recorders, on the other hand, do not perform format conversions when hacked: if you "region-hack" a recorder, about all you accomplish is having the thing not spit a Region 2 disc out as soon as you load it. You might as well not have bothered.
Your problem is your hacked Sony 780 now accepts region 2 discs for playback, but it is playing them in the format they were originally recorded as: PAL. Some North American televisions can handle this, and will convert the image for you seamlessly, but most like your Samsung cannot process a PAL signal and will throw a "not supported" alert on screen. Your two options are to either replace the Samsung with another set that converts, or forget using the Sony as a playback deck and buy a proper multi-format multi-region converting DVD player. If you don't have a lot of PAL discs, a simple $39 Phillips dvd player at Wal*Mart should suffice, if you have a huge PAL library you might want to opt for something nicer like an Oppo which runs about $200. In any case your Sony 780 is designed as a recorder first, with playback being a distant second consideration. DVD is not like VHS, where all machines were dual-purpose record/playback devices: dvd recorders are easily worn out prematurely if used as players and burner repair costs more than the entire recorder did. Anyone with a dvd/hdd recorder really ought to have a separate dedicated dvd player to reduce unnecessary wear on the recorder and to play the many odd PAL and DiVX formats most recorders have trouble with.