Q&A

I recently cleaned th MAF with MAF cleaner or at least I think I did. Now the car won't start, it cranks but won't turn over and the cooling fan is running. The diagnostic that I ran on it previously, before I began attempting to "fix" (or as my kids say, "breaking it more") anything and got the following codes: P0115, P0115, P0420. I can't afford to take the car to a mechanic. It doesn't seem to be beyond my ablitiy, or lack of it, to at least replace these 2 sensors, but a "how to" or "if I should" would help, PLEASE