Dear Andrew,
Have you been putting hamsters in the VCR? May sound odd, but it is a common cause of loss of pictures. My advice is, keep rodents out of the machine - videos only, no matter how tempted you are by the site of the furry little fluff balls disappearing into the slot.
Another possibility could be that your vcr is haunted, although you would usually get some picture - most likely of a headless child, or similar. Try saying twenty Hail MAry's and dousing the machine on holy water, just to be sure.
Dr Lois Lane., April 2007