Hi:
This maybe an insult to everyone's intelligence. However, have you checked the scart connection at the back (the one with the metal retaining clip over it) and ensured that this is plugged in properly. This happened with my machine - sound but no picture. Took the cable out, blew it, pushed it back and it worked fine. That is until recently it broke all together and now there is no power to it.
I have a spare VCR mech to replace the old one in mine but I haven't built up the courage to take my TV apart for risk of breaking it further. If you pay the postage you could have my new old mech. However, I cannot guarantee it working as I salvaged it out of an old set with a broken tube. The owner assured me that it worked the last time they used it however.
Graham