Forget the steam cleaning for now. Your first step should be to get that carpet up out of the downstairs and lay it out on the driveway upside down on a sunny day for a few hours. While that is going on, take a bleach solution to the floor where the carpet goes. (1 cup to a gallon) Next, (and I am assuming your carpet has jute backing) take a garden sprayer and lightly spray the same strength bleach solution to the back side of the carpet. Let it dry and reinstall with a new pad or no pad at all might be better. I assume you have a dehumidifier to dry out the basement. If not, get one or use your central air if you have one. Now having said that, maybe you need to consider a battery back up for that sump pump?.... Good luck, Dodgeman