Sean colgan, it seems most likely that the problem is either the backlight or the power supply for it. Samsungs have a well-known issue with bad caps in the PSU section. Check those first. Of course you do want to make sure that your TV is unplugged. Leave it unplugged for a couple of hours (overnight) Of course you also want to try a different video source. More information when we know what model this is.

Check the diodes on the power supply. Those have a tendency of failing on this model.