When i collected all 4 Aetherium Shards and went to the Ruins of Bthalft Katria didn't appear.
I placed the shards in the mechanism anyway but, as i already told, Katria did not appear and there was no earthquake. After the quest updated to "stand clear" i went to the questmarker and nothing happened.
I tried fast traveling back and forth, and when i fast traveled back, the tower did arise after all and Katria appeared but this time the elevator and the lever wont appear so i cant enter the forge.
I tried google to solve the problem but it seems im maybe the first.
go to Bthardanz there is a shine across a bridge over a waterfall, where the afflicted are living. aside from the aetherium shards you also need the Dwarven sword and helm before you are granted permission to enter the elevator. after returning to the elevator with Katria she will instruct you to place the shards in the statue then tell you to get off as it begins to rise from the ground.(stand next to her), when the ground stops rumbling then use the elevator with Katria inside it. then continue with the game...
sorry AzuraKnight but it is required as is stated within the lost to the ages direction as seen/copied below;
Deep Folk Crossing is a Dwemer bridge going over the river. The player needs to locate this landmark and venture across it to retrieve the last Shard atop a plinth (along with a Dwarven helmet, Dwarven sword, and a Dwemer Convector). Upon doing so, Katria will tell the player that all that is left to do is find the Forge.
I ignored the sword and helm completely and finished the quest with no problem. The only reason they're there is as decoration and loot around the convector use for the quest Arniels Endeavor that little Dwemer shrine and the said items at Deep Folk Crossing were there before Dawnguard was even released.
yes the shrine was there before the dlc's and I too also completed the forge without having to insert the convector, but maybe the independent glitches we have in our games are not the same for the person posting this thread and therefore needs all pertanent info to assist his completion of this quest.
I glad it worked for you and you could do the quest but i still can't see how the sword and helmet had anything to do with the Atherium quest. The quote Prometheus used didn't say anything more than the items just happen to be around the one you actually need, people have ignored them and finished the quest (as did i). Whatever fixed your quest probably wasn't that.
I had this same problem, and finally found a solution (online). I can't take credit for this, but it sounds like this bug is still affecting many people so I wanted to share it.
To confirm the 'problem', this is what was facing: I collected all the Aetherium pieces (no need for the misc dwarven parts), placed them on the Bthalft pedistal, the elevator rose up, but there was no elevator "lever" inside. Just flat floor. TCL confirmed there was nothing in or under the elevator that was helpful. Kat was there, but she was stuck saying "go ahead, try it".
So to fix this... start by making sure your 'setstage' is completed enough to perform this fix. To do that, open the console, and type the following:
setstage DLC1LD 160 (enter)
setstage DLC1LD 170 (enter)
setstage DLC1LD 180 (enter)
setstage DLC1LD 185 (enter)
setstage DLC1LD 187 (enter)
Then, type this in the console:
coc DLC1BTHALFT01 (enter)
This will get you into the Forge. Kat will auto-follow after a moment. There is an "elevator lever" to get out to Skyrim, but if you leave there is not one go back down to the Forge. If you leave the Forge, you will have to use the 'coc' method again.
Once you are in the Forge, finish the quest as normal.
Have you defeated the Forgemaster? It may be one of the problems if you haven't. If you did, then try speaking to Katria again, or leaving the forge, then coming back. If all else fails, reload from before the boss fight.