Started in Morrowind but feel like starting some Oblivion quests now. Wandered over to the place where you exit the sewers, see the blood stain but there is no dead guard. I am guessing I entered the cell a few weeks ago and he triggered and now his body evaporated. Any way to bring it back?

#1
Try this in the console:
CATdeadknight.enable
Maybe he got disabled somehow. If that doesn't make him appear, enter this stuff in the console, one line at a time, to start the main quest:
addtopic BladesTopic
addtopic MehrunesDagonTopic
SetStage charactergen 88
SetStage MQ01 88
Player.additem AmuletofKings 1
Also, to help me fix this problem, can you tell me what you did to start the game/character that you're having trouble with?
Was Morroblivion installed when you started your current game?
What method[s] have you used to travel between Morrowind and Oblivion worldspaces, or was it ONLY with my CAT mod?
What exact path did you take to end up here? (for example, "i started this game using the CAT mod's Vvardenfell Quick Start, went to Cyrodiil using the CAT mod's transport guide (Jo'Tesh), and no knight was there.)