Still not sure if Toriver and I are having the same problem, but I discovered that the issue I'm running into can be resolved quickly by turning off kernel modesetting.
If you think you might be experiencing this same problem, you can test by turning off modesetting temporarily at startup.
To do this:
1) Reboot your computer and hold down the Ctrl button. This should bring up the grub boot menu. If you see the login screen, you've gone too far.
2) hit 'a' to bring up the kernel command line\
3) add "nomodeset" (no quotations) to the end of the line.
4) hit enter
You should see a weird little blue and white bar go across the screen as fedora boots. After that the login screen will come up, and you should be able to login normally. If you can watch videos without any problems now, kernel modesetting was probably the culprit.
As a non-expert in kernel modesetting, I have no idea what advantages it offers other than giving you a shinier bootup screen, but there is a page about it here
If turning it off makes your life better and you want to do it permanently, just put the nomodeset command into your grub configuration file like this:
1) su - [or sudo]
2) enter root password
3) gedit /boot/grub/grub.conf
4) grub.conf will open in a text editor
5) look for lines that start with "kernel" and probably ends with "rhgb quiet" unless you removed it. (There are probably between 1-3 of these lines).
6) add "nomodeset" (without quotations) to the end of these lines
7) save and close
If someone who knows something about modesetting tells you that you need it, listen to that person and not me.