Movies no longer playing

Since my time in SL I have enjoyed watching movies regularly with friends. I have had no problem with this from day one, good quality, good sound, and almost immediate start time when a movie loads to play.
Last week I bought a new selection of DVDs in SL and watched one on Thursday perfectly. On Friday, nothing. The tv screen at my home remained plain black with the default texture, no sound could be heard, and I had extended lag waiting for it to load (twice having the viewer close on me). I updated Quicktime, tried different movies, even went to other sims, and still no movie picture and no sound. However, I can watch YouTube vids with no problem at all.
Several visitors have come to our home to check this for me and each one of them could watch the selected movie without a problem, and I still had extended lag and no movie or sound.
I have tried with both the Emerald and the standard SL viewers, and have not altered any of my settings at all.
Has anyone experienced anything similar lately and is there any fix I could use?.

Have you cleared cache? You might have a funky link/corrupted file in there somewhere.

Thank you, yes, I did clear the cache and do so at least once a week.

When you say "went to other sims" does that mean you took your TV back into Inventory, then rezzed it in a different sim, then tried to play movies?

If not, what happens if you do that?

Update quicktime. A new version just came out.

No, the tv is not owned by me and so I cannot operate it, but have had no problem at all with any tv set we have used this year. In fact, we use two, one for YouTube (and sometimes moves), the other for just movies. Visitors are able to view and hear movies on both of those tv sets but I am not.
By going to other sims, I meant going to other places where there was a movie playing. Those with me were able to view the movie, I was not.
By deduction, I say the problem is solely with me and yet nothing at all has been changed on my settings. Plus, I did re-install the Emerald and SL viewers just in case of a problem and there was no change.

As for Quicktime, yes, I updated it less than 24 hours ago to the new version, and it made no difference at all.

I've had some oddities occur similar to that, and I'm unsure if it is the fault of the script in the DVD or SL acting up. I usually just tinker with it awhile and get it to work. For example, I'll hit play in the DVD menu, I'll see a message "Vance Adder has started playing the movie", but my movies controls will stay grayed out indefinitely. I can try over and over again with no success. Last time that happened, I manually copied a movie stream into the media settings, *THEN* hit play on the DVD, and it fired right up.

Ahh, but in my problem, nobody could see the movie... it wasn't just me. Once I fixed it, everyone could see it fine.

What about updating the drivers on your video card? Might as well try it...

Thank you guys.
Each day I have tried to watch movies, either from those stored on a DVD player and also those lying lose and not loaded to DVD.
All gave me a blank screen.
A few minutes ago I tried again for the second time today and, although not having changed one setting, all movies started within seconds, I could see the pictures and hear the sound, and on both of our tv with different media textures.
I have no idea why it all suddenly stopped playing, and have no idea why it has all suddenly started playing again.
But thank you all for your assistance.