He didn't "power down" he tore off his demonic helmet. He still had all the Cyttorak spikes going on. At the end of the day Collosus' job was to take out the Red Hulk. He failed miserably like he always does. If you have this super powerful guy but whenever he uses his powers he shuts down because he is afraid, what use is he? None.
Oh my God. Either read the issue again and pay attention this time or take it to rumbles. No one here want s to explain what's clear on page to you.