Make sure you have the latest version of Flash Player installed
If you have the latest Flash Player, or you just installed the latest Flash Player, and for some reason you still have the same problem try this:
It's very possible that your directories of "Temporary Internet
Files" and RAM (sometimes known as "cache") are close to
the maximum and cannot take anymore, the end result
being any of the above scenarios or videos that:
A) come to a complete freeze;
B) start/stop/start/stop in a choppy way;
C) never even make it onto your screen.
Exit out of YouTube, then clear your "cache" of all its
"Temporary Internet Files", "Cookies" and "History". It is best
if you shutdown and reboot afterwards. Internet Explorer :
→ Tools → Internet Options → Delete...
→ Delete files → Yes
→ Delete cookies → OK
→ Delete history → OK
→ Close (browsing history window)
→ OKMozilla Firefox :
→ Tools → Clear Private Data
[x] Browsing History
[x] Download History
[x] Saved Form and Search History
→ Clear Private Data Now
..Go back to Youtube see how she is now.