This can be fixed although it may take an hour or so - AND YOU DON'T NEED TO PAY OR BUY ANYTHING!!!
THIS INFO IS FOR PEOPLE WHO DON'T KNOW ABOUT COMPUTERS.
I'm 52 and only involved with computers for the past 10 years. As time passed I was shelling out brain surgeon fees to "computer experts". So just as I did with cars, I learned some things for myself.
This info is all over the net when you type in this question. What if your script is already set at Enable and it still won't work? You need to go to Adobe on your computer - remember I'm writing this as a geek for other geeks to understand - click start, your menu appears, go to Programmes contained on your pc, look for all the programmes you have on your computer. There will be a long list of programmes like Internet Explorer, Games, Java, Media Player all in alphabetical order. Go to Java and make sure it is Enabled. If not, then enable it and you are sorted!
You do this and still can't watch youtube.Go to Abobe and download Flash Player 10. If you do and it looks like you have downloaded it - the page says "you have successfully downloaded Adobe Flash Player 10.0... but you have the same problem - then you must go to your pc Security system, Norton or whatever it is. Click on it til it comes up on your screen. Disable everything. It will warn you you are unprotected etc., but don't worry you're not going to be threatened. Shut it all down, ie change the settings to leave your pc without protection. It will ask "How long do you want to remain unprotected?" Reply "Until I tell you" because you might need some time. Go to settings and remove the firewall, security inspector and anything that is stopping you from downloading the java or flash you need. THIS IS TEMPORARY BTW DO NOT DISARM IT PERMANENTLY. Once your pc has no protection it will allow the downloads you need through. The pc security thinks it's helping you but all it's doing is causing more problems by blocking what you're rtying to do. In fact, if you look at your security report it will tell you it's blocked Adobe and if you've done it a couple of times it will treat it as an attack. Go to Abobe's page on the web. Now you are going to need to download the programme that lets you UNINSTALL whatever Flash Player you have. Clear it out and then install the up-to-date one. Your machine is confused so clear the system of Flash and put in the new one you download from Adobe's site.
You're home and dry. This takes about an hour in total, but when I did it the first time it took about 10 hours!
Reset your Firewall, blockers and security.
Hope this helps those who don't know too much. Please consider becoming a socialist and lets make the world a better place.