Well, Clark's lost his powers before. The general DC stance is that he's a hero with or without them, and that even when deprived of his physical strength, he still has a vast reserve of emotional/character strength. He gets frustrated and such when he can't do the things he's used to being able to do, but he pulls it together and does the best he can with what he's got. After all, he's Superman. It's what he does.
I remember there was one ep of Superman: TAS (the 90s cartoon) where he lost his powers because Dr. Light (the guy who blinded him in L&C) had set up a force field of sorts around the Earth that blocked out some of the light coming in from the sun, fixing it so that, for all intents and purposes, Earth had a red sun.
There's this great scene where powerless Clark tries to shave. He doesn't really know what he's doing, so he nicks himself. And practically jumps from the unaccustomed sting of pain. He blots it with a cotton ball, but he's pretty disgusted with the situation. He lets it out by throwing the cotton ball with all his might... and it lands gently in the trash, which just serves to underline the situation even more. He growls, grips the edges of the sink... and then goes back to the task at hand.
Not exactly heroic, but it's the best representation/demonstration I've seen of Clark's frustration with powerlessness.
