After some time off I am doing the Morytania tasks. I am on the Hard ones and I am stuck on

 

"Detarnation" Kill Tarn Razorlor (or visit his lair if hes already dead). Haunted Mine 40 Slayer

Suggested: Ring of slaying

Travel north through the Haunted Mine to reach and kill Tarn Razorlor. If he has already been defeated, you may use a Ring of slaying to teleport to Tarn's Lair. Note that you will be teleported outside of the terror dog room before Tarn's lair.

 

I am in the room with the Crystal mine key and I have picked it up. I did the quest forever ago. Where did I go wrong?

That's not where Tarn is. Tarn is in a separate section of the Haunted Mine that isn't used during the quest. Get a Ring of Slaying and use its teleport option and that'll take you right there. (You could go through the whole maze, but it's a humongous pain in the neck, so it's much better to skip it with the ring.)

Alternatively, if you have no ring of slaying, you can just take the long way and tip.it can show you how. If you do it this way, you'll want to bring some food and/or prayer pots.

 

Leave the mine and go back in through the entrance that requires jumping over the mine carts. Then follow this simple line: http://www.tip.it/runescape/?page=tarns_lair.htm#walkthrough

 

Then just scroll up to see the path to take to Tarn's liar. Just BE CAREFUL! There are a lot of spikes and traps that pop up. The damage from that + zombie attacks can kill any player if they aren't paying attention.

 

Good luck!