I've run into this problem and it's actually quite easy to fix.
First you have to pull the 3rd lever from the left on the west wall. This will set off a magic static cloud that you'll need to avoid, since touching it will cause decay. The lever will cause one of the stones in the east wall to fall out, revealing an ornate key. Use the key to open the left door on the north wall to enter the room that seemingly is empty, but it's just an illusion by the Lava Sorceress! From the door entrance, move north 8 steps, east 3 steps, then north 4 steps. This will put you on the invisible pressure plate that will cause the chest to materialize in the previous room. Be careful when going back to the other room because Fire Mages will spawn and shoot Level 25 Inferno spells at you. They're linear, so it's easy to side step them, or just block them with the Blaze Shield that the Blaze Knights drop. After defeating the Fire Mages, open the chest for the Rod of Might. With the Rod of Might, you can access your Steam settings and change your profile picture.