Why have all my photos got a black shadow on the top?

I woke up one morning and started taking photos and from there on all the photos I've taken (for the next 2 days or something) have had a dark black shadow round the top of them. When I'm looking through the lens there's no band just after I've taken the photo. I've uploaded them onto the computer and the same problem happens. So I'm guessing it's either something to do with the shutter or a setting. If I put the shutter speed lower it tends to make the dark band go away a bit but not completely.
I'm using a Nikon D70

Without any examples it's difficult to diagnose but it sounds like the shutter is failing

The best thing to do is take it into a Nikon authorized repair center (or send it to Nikon) for an inspection.

Are you using flash? This is a common issue with using a shutter speed too fast for flash sync.

If you aren't using flash, then your D70 is having another shutter issue, and it may be time to look at a replacement.