No sound, I can record to HDD but there is no audio, why?

Check the sound setup to TV. Refer its user manual for details. Check whether the audio format to the recorded disc do match with to that of TVs.

Troubleshoot: Unless you already did this, go to Device Manager and check the properties of all other hardware involved.

The control board is shot including the on/off switch.

It's on the Toshiba website -

http://www.toshiba-om.net/DVD/PDF/English/Country_Specific/RDXV59-English-Specific.pdf

be more specific please. Normally you could use A/V cables to your dvd recorder then from dvd recorder to TV.
from your signal that feeds to your tv just feed to the toshiba dvd recorder, then from dvd recorder to tv, then you should be golden. Just dont forget to set the channel on the dvd recorder.

Switching off DVD & disconnecting at mains cured the problem.

My machine has also done this since it was new. I was just about to bring it in for repair when I thought I would try one more thing. I turned on the recorder. I put in the movie that would not play and let it load (of course it would not load). I pushed the on/off button on the recorder and held it down until the "wait" message came up on the display. After the message disappeared I turned the recorder back on. To my surprise the movie loaded and played. I tried all the other movies I had trouble with and they also played. I hope this helps. I saved my self over 200 dollars in repair bills. I was quite surprised at the lack of help from toshiba.

time to buy new one or upgrade software
new cd/dvd formats came out maken it hard to play record or watch on outdate equipment
they remolded the cd/dvds with a new gloss

Tyr using -r dvds ,,,,,that might resolve your problems

As mentioned on the Jan12 e-mailed Panasonic - surprise, no response! However on Panasonic's web site drill down to firmware upgrades for DVD machines. There is an upgrade available for the E50P. Straight forward fix, download to computer, expand it and copy to a CD-R. Put CD-R into E50 and recorder will check and update firmware. I did this on the 13th and have recorded two commercial free movies and both have played back perfectly after finalization. Time will tell. Hope this helps. Golferdon