My computer has some corrupted or incompatible files that keep it from running any games because the graphics don’t work. It otherwise seems fine. I should get a new one anyway, but I’m unclear as to whether Steam really backs up save files on Avernum or just achievements and stuff (I’ve read that it doesn’t save the save files). I didn’t realize that might be an issue, so I might have screwed up my game trying to un-install and re-intall to fix the problem. A friend who’s good with computers gave me some ideas, but I haven’t gotten to trying them yet.

In the castle, talk to the Wizard Rone. Have you spoken to him? He’s in the South West of the Castle.

The Orb is in the dungeon called The Stagnant Tunnels. I think this is the entrance: https://lparchive.org/Avernum-Escape-from-the-Pit/Update%2034/54-avernum-30-048.png
Is that where you are? It’s in the Waterfall Warren. I don’t think you need to do anything to trigger it access to the dungeon.