TVout Blocking signal?

[ELBEARDO69]

Ive recently started using the TVout on my Geforce card to extend my desktop. From working perfectly, the picture on the TV now flicks between perfect one second, then rubbish the next, i.e it goes quite dark, blurred and decreases slightly in size. Any ideas what this is. I only have the problem so far in ME, works fine in 98se.
Ive seen the same thing on the copied tape, when VHS movies are copied back to back using only a scart lead.

Cheers