Why doesn't the time and date appear on my photos anymore?

When the camera(Nikon D40) was new the time and date appeared in the lower right hand side of my photos but that stopped abruptly.

The option to timestamp pictures is available when you connect the camera to a PictBridge printer
(Page 59 of your manual)
Also check the set-up of your printer to see if it can timestamp the photos when printing --mine can.