wont turn over, need help with gauges too

my car is a 95 neon coupe with a 98 dohc motor, computer and wiring harness and it was running great and all of a sudden wont turn over at all, ive checked everything, the fuses, relays, wiring and i know that the starter is good because i just recently put it in. second problem, i bought an autometer 5 inch tachometer, air/fuel ratio, water temp, and oil pressure gauges and am having trouble with them, the tachometer always jumps to where the shift light is set but sometimes works fine, second issue that im having is that the air/fuel gauge stays lit up all the time, even with the key off, ive hooked the ignition lead to 3 different switched ignition sources and i keep having the same problem, any help would be great. thanx for your time

Checked you battery connections and grounds?

Check your trans. shifter cables if they're gone you'll have to get new ones
P.S. dealer items only

my trans cables are good, i just put them in a few months ago and havent driven the car yet with them. also i checked all of my grounds, wires, fuses, battery terminals and clutch sensor and nothing is wrong with them, i have been having tons of problems with the starter and battery wires lately tho, ive changed them like 3 times in the last 3 months. my car is also throwing a trouble code 12 which is something to do with power loss to the ecu over the last 50 key on cycles. im also throwing codes 21 31 and 35.

did you find the problem