User blog comment:Memeber/Lost to the Ages does not start/@comment-28529499-20160530193839

I found these fixes, there are more but check these out first:

This quest may not start if, after installing Dawnguard, you have visited Mzulft or Deep Folk Crossing prior to reading The Aetherium Wars and the corpses at these locations have been fully removed from the game.

PC Only This bug is fixed by version 2.0.1 of the Unofficial Dawnguard Patch.

After forging either the crown, shield, or staff at the forge, the quest may not update and you will remain trapped in the room with the forge as the stairs won't come back up.

Use setstage DLC1LD_Bthalft 90 in the console.