According to Jim Recap: The Closet
One morning as Jim tries to shave, he finds that Cheryl has unplugged his razor, and then he notices that she has completely invaded his side of the sink. Getting dressed, he sees that her clothes are taking over his side of the closet. It's like he is being pushed out of existence, with nowhere to call his own. So he pulls out all of his old junk and redecorates their room with neon and sports memorabilia - even a scoreboard over the head of their bed. It's really bad. Cheryl retailiates by turning the garage into a yoga studio. It's on.
Of course this leads to a fight, but for once it seems that Jim has given in. He takes the things out of the bedroom and restores it to the way that it was, and Cheryl seems genuinely touched by the gesture. As he heads up to the attic to put the final touches there, it looks like this is one fight that will end early. Then the music starts. Jim has turned the attic into his personal space!
Unfortunately, he forgot not only that the attic stairs can be closed from downstairs - which Cheryl does - but that the power comes from the extension cord that he also ran downstairs - which Cheryl also unplugs. So he and Andy are in the attic in the dark with no way out. Whoops. Before long he starts banging around, and then he falls through the ceiling and onto the bed. Perhaps that wasn't the best strategy.
