I don't seem to do much damage, so I figure this is going to take awhile. alduin gets back up and tries to fly again, so I hit him with dragonrend again...he lands and I whack at him. This goes on for like 20 minutes. I die every 4 or 5 minutes and have to start over. Then I start to think that the main quest is bugged. In fact, I had just gone to (something) Hearth Barrow or whatever and the pedistals would not turn. Then the 1.3 update came through, so I figured I'd wait and see if that fixes anything.
I go back into the game...the Hearth Barrow pedistals turned this time.. OK...I figure the update fixed everything. I go back to the Throat of the World and resume my attack on Alduin. Another 20 minutes and I have yet to see any sign that I'm doing any damage to the dragon. I finally, search for a walkthrough because the forums were down at the time. Come to find out it's impossible to kill Alduin by myself...I have to do some other main quest stuff to get others to join me! Good Grief!
the other dragon should have said something like, hey...you can't defeat Alduin without help...go do (whatever) quest before you die. Something to keep us from spending an hour trying to kill a dragon that the game won't let us do.
