Hello, I'm TV Tech1 and I'll be working with you to identify and help you resolve your problem.
Sound loss on a TV set that can be recovered from by turning the TV off and on again is usually created by HDMI connections, and partial loss of the datastream. That may simply be a situation where you have to unplug the TV and the box delivering HDMI to the TV set, waiting 20 minutes for them to reset, and then powering BOTH back on with the HDMI cable disconnected.
Then you wait one minute and hot-plug the HDMI cable back in and restore the handshaking between the two units. That's worked on several brands of TV, especially Sony and Samsung. Toshiba TV sets aren't as popular as those two brands, so most of our calls have been on the other two. It seems to recover on them.
One other issue I've seen is the actual connectors on the HDMI cable are pulled down due to the weight of the cables or they're push up against a wall causing poor contact. I don't think that's your issue, but I have seen that happen too.
As for warranty...it's usually one year. They don't include the warranty in the customer handbook as it usually printed on the warranty card you send into the manufacturer, or on a separate sheet with the warranty card. The best way to know what your warranty is, is to contact Toshiba directly and see if the warranty is one year or if they have a two year warranty specifically for your model. I rarely see a two year warranty but some models do have them if they are the high end models.
I'm not too keen on giving you the Toshiba Customer Service number because they keep stating £8/min to call 0871(NNN) NNN-NNNN9am - 6pm. They're the first company I see charging for customer service. Email enquiries seem to be free.
Try the reset, let me know if that restores your sound, ok?