You'll no doubt get more specific advice but I recommend you try this Firefox extension for a short term workaround at least(I use it all the time). It plays nearly all YouTube Videos in HTML 5 - without Flash.

https://addons.mozilla.org/en-US/firefox/addon/youtube-all-html5/?src=search

I don't think it's flash. Flash Player crashed twice since, and I got a fair share of non-responsive shockwave dialogue boxes here and there. (And this is only night number 1!)

As I mentioned, aside from the two crashes, Gogoanime, a video site, has been working fine for the past hour or so. I've been watching subtitled anime, since I have no speakers. But no YouTube, and no DuelingNetwork. These are my 3 most common sites that use Flash.

@alan_r:

I added the add-on you suggested. I watched an entire Youtube advertisement. When the video started, it glitched out as usual. But... a YouTube ad is a YouTube ad. That's an improvement, if only a slight one.

Well, I'm pretty much ready to deem this computer as a lost cause. I just bring it in to be repaired next month.

I've been away from my computer. I had hoped someone else would pick up the threads. Please don't give up just yet. I presume you've tried various items on YouTube. If you haven't done this yet, you should do the computer equivalent of "kicking the car tires " - reboot the computer and re-start Firefox and YouTube several times. Have you tried a different browser? You can download Google Chrome or Opera very quickly. I'm puzzled why you don't think Flash is at least part of the problem. You should remove it re-instal it.

Are you having any other problems that might give us a clue?

Then you should go to Help and work through the various troubleshooting suggestions including Safe Mode and creating a New Profile.

I'll be away for a while and, in any case, I really only joined in to offer a workaround that I hoped would work.Major Contributors should be able to help you solve your problem.