Rep Power: 743

Okay, first my o2 sensor went out giving me the p0130(I believe that's what it was). Fixed that and SES went out for like 2 days and returned. Of course emissions wouldn't pass cuz of that. Next went to get it read, it was o2 codes again. Had them deleted and codes went away for like 4 days. Of course, as I was going to emissions to hopefully pass, code came back. This time code of P0420. That being the cat. Had that code deleted so it wouldn't read and setting set to Ready. Went to go do emissions and it failed cuz the SES won't light up from the MIL(whatever that is). I'm not sure what it is. It stumped Horist and all. I have a 1998 z28. Maybe it's cuz I got a car from that year, but he used HP Tuners to delete the codes and set my stuff to Ready. Does anyone here know what it could be?