1280x1024

1280 x 960 seems fairly normal -- i.e., a 4:3 (1.33:1) aspect ratio while 1280 x 1024 is a bit more unusual -- i.e., a 5:4 (a 1.25:1) aspect ratio. In any case, not sure if you are referring to an HDTV monitor here or a regular computer monitor. In either case, the settings would have to be "negotiated" between the TV and monitor devices to become available. In the case of an HDTV monitor, I assume this would require you to be plugged into the "computer" input interface for any such negotiation to even take place. If you were previously connected in this manner and then switched inputs, then that might explain your no longer being able to use these dimensions.