93 240sx sr20det starting problmes need help!!!

[240sxs1377]

well went out to start my car today and i turn the key and click her some buzzin in my engine bay so i let off. open the hood and notice my starter cable i loose so i go back tightne it down and still nothing just a click. also my rpm gauge is going crazy it keeps on going to full redline then back to 1. i checked the ecu codes and at first it sad 11 which is a problem with the cas. but i turned off the key and back on and checked the codes again and it went back to 55 which is all good. is my starter bad? and whats going on with my rpm gauge i noticed it had been doing that earlier but when i start it goes to normal but thats when it would start.