I have a quest from the Thieves Guild. I must investigate his house, getting passed the guard named Vald. I did a small quest to get him to move. I went to his location and found his body on the floor outside. How to I get him back to open the barred door to the house?
If his body hasn't disappeared, he should have the key on him.
But there are other ways to do it even if that doesn't work. On the back of the house there is a lever you can hit with an arrow that will cause a ramp to the top story to unfold. The door up there just has an expert lock.
There's a YouTube video demonstrating both of the above (warning: the house's owner is a spoiler).