Much more detail is required to have any chance of answering this one I'm afraid. Otherwise we'll simply be stabbing in the dark for days/nights. The sort of information required is:
What's the make/model of the DVD recorder?
How have you got them cabled up: Sky-to-recorder, then recorder-to-TV, or something else?
What have you got connected to the 'TV' SCART socket on the Sky box?
What have you got connected to the 'VCR' SCART socket on the Sky box?
Have you configured the Sky box to output RGB? Or PAL?
Which SCART connection are you using for Recorder IN?
Have you configured that to input RGB?
Which SCART connection are you using for Recorder OUT?
Have you configured that to output RGB?
Does the recorder work OK on playback?
If you select System Setup on the Sky box, does anything come up on the TV?
Have you tried different SCART leads?
Have you checked they're thoroughly plugged in and havn't come adrift when moving the box(es)?
Is there any sound output from Sky channels, or is it video and audio that's missing?
Have you tried connecting the Sky box directly to the TV? (In case the Sky box has failed).