Weird thing going on with Flash and IE

I like to watch playlists on Youtube, but for some reason when I've been watching vids for a long time, after several videos it stops working. Sometimes it just hangs, but here lately there's been a message that pops up telling me I need to download Flash player, never mind that I've just spent the last hour watching vids with Flash. When I close and then restart IE, it goes back to working normally for the next several videos until it decides again that I don't have flash player. It even plays the video I just tried to watch before I closed the browsing session. I've actually got the built-in flash that comes with IE, plus the latest flash player from adobe's web site because I just recently attempted to switch to Firefox. Flash also does this when I listen to other audio or music that uses it, but it doesn't seem as bad. It seems to allow me longer time to use the player before I get the dreaded alert icon. This is really strange, as I just got this laptop.