If you keep getting "HELLO, YOU EITHER HAVE JAVASCRIPT TURNED OFF OR AN
OLD VERSION OF ADOBE'S FLASH PLAYER....GET THE LATEST FLASH PLAYER":
don't bother downloading and re-installing the latest Flash over and over and over again.
You will get absolutely nowhere doing that, because that is only adding to the problem.
Your YouTube was working fine just a little while ago, right?
There can really be only 3 possibilities:
1) something is wrong with YouTube
2) something is wrong with your cache
3) something is wrong with Flash 10
1) YOUTUBE:
Your problem may fix itself within a couple hours, or by the
next day, because YouTube often "shuts down" a bunch of
their own servers every single day without warning anybody
in order to update all kinds of stuff. During those occasions,
it's YouTube's transmissions of "JavaScript" or "Flash" that
are poor -- not your reception of it. This sometimes creates
"time-out" or "run-time" errors, and can be solved by hitting
"F5", "Refresh", or "Back" & "Forward" on your browser.
2) CACHE:
If the following day your YouTube is still stuck and showing
you those awful "JavaScript" and "Flash Player" messages,
it's possible that your sub-directories of "temporary internet
files" and "cache" memory are full, and won't take anymore.
Thus videos cannot even buffer or make it onto your screen.
"Temporary internet files" are 1000s of tiny bits of websites
permanently put on your computer's hard-drive. They'll stay
there forever and ever, gradually plugging up your computer
(like hair slowly clogs a sink drain) until you get rid of them.
Because your computer now has such little space in which
to "cache" a video, YouTube will mistakenly think that your
Java Script "run-time environment" or "buffer overflow" is off,
or that your Flash player (unable to absorb those videos) is
older than "FLASH 7".
The solution to all that is to exit YouTube (but not your web
browser), then clear your "cache" of all its "TIFs", "cookies"
and "history". (See below.) After that, shutdown and reboot.
3) FLASH:
Watching YouTube vids hasn't changed in the past 2 years.
(You could still use Flash 8 if you want to.) It looks like the
newest Flash players are causing many YouTubers a lot of
grief, especially all 8 variations of version 10.
It's absolutely nuts that there's 10.0.525, 10.1.218, 10.2.26,
10.2.54, 10.12.10, 10.12.36, 10.15.3 and 10.22.87. Usually
most updates are good for only 1 thing:...Software conflicts.
I've never strayed away from 9.47, and many "flashers" use
9.45. Think of those 2 Flashs as Windows XP compared to
Vista. Look at what the Asker wrote to this answer of mine:
https://answersrip.com/question/index?qid=20081125075929AABZpVS
If that seems interesting to you, here is the appropriate link:
http://www.oldapps.com/flash_player.php?old_flash_player=14
Note 1: if you've got an "Accelerator", dump it, burn it, rip it,
kick it, trash it, disable it, uninstall it; do all that you can to
get as far away from it as possible. Several "Ad Block" and
"Messenger" programs also conflict with YouTube.
Note 2: longer videos may require "Flash" and "Shockwave"
to play proper. You don't need anything else -- so avoid the
sales pitches some Yahooligans are shilling, because they
are really disguised salespeople & peddlers. Their answers
have nothing to do with your question, and their wares may
actually worsen your problem. Besides, what kind of idiotic
answer is "Despite the fact you can't even watch or access
videos, buy our downloader." [my paraphrase]
Note 3: a very odd fix that once worked for me was altering
the URL from "www.youtube.com" to simply "youtube.com".
Note 4: if you downloaded Flash, did you actually INSTALL
it afterwards? If you got Firefox, did you enable the add-on?
I hope that my info and long answer are quite helpful to you.
Internet Explorer 6:
→ Tools → Internet Options
→ Delete Cookies → OK
→ Delete Files → OK
→ Clear History → Yes
→ OK
Internet Explorer 7:
→ Tools → Internet Options → Delete...
→ Delete files → Yes
→ Delete cookies → OK
→ Delete history → OK
→ Close (browsing history window)
→ OK
Internet Explorer 8:
→ Tools → Delete Browsing History
[. ] Preserve Favorites (leave blank)
[x] Temporary Internet files
[x] Cookies
[x] History
→ Delete
Mozilla Firefox 3:
→ Tools → Clear Private Data
[x] Browsing History
[x] Download History
[x] Saved Form and Search History
[x] Cache
[x] Cookies
→ Clear Private Data Now
Google Chrome:
→ Tools (wrench) → Clear browsing data...
[x] Clear browsing history
[x] Clear download history
[x] Empty the cache
[x] Delete cookies
Clear data from this period: → Everything
→ Clear Browsing Data