I seem to have killed my ute, and I've got no idea what the hell has happened so let me fill you guys in with the back story and maybe you can help me out (It's a 98 XH Falcon Ute).

A few days ago I had a flat battery, so I replaced it no problem at all until I get into the car and realize that the original cassette tape displays "CODE", which I have heard about before but since I didn't have the code, I decided to replace the cassette player with a used cd player I had in the shed. Wired it all up, car would start, but I couldn't get the CD player to work so I figure that it's been damaged at some point, take it out and tape up all the connections until I can buy another stereo somewhere cheap.

After I was done, I tried to lock the doors using remote keyless entry, but it's not working for some reason, so I go and manually lock the doors thinking I'd try to figure out what it is laster. Yesterday I got in the ute to drive it somewhere, and the engine turns over beautifully but the car WILL NOT START, it's almost as if the car isn't getting petrol? I did some research online trying to figure out what it might be and there are a few causes, but I'm wondering if somehow I've set off the smartlock immobilizer (if it has one?) and whether this might be my issue, and if so how the hell I fix it - I just find it weird that I removed the cd player, worked fine, wired it all up and suddenly remove keyless fails, and the car will turn over but not start. I've checked the fuses, everything is good except for one coming off the positive terminal, but I have no idea what that is so I'll go buy a couple today and try it when I get home, in the mean time I'm hoping for some advice.

I'd really prefer to avoid having to get it towed to somewhere to get it fixed, but that might be the bottom line if I can't figure it out, I'd really appreciate some tips (dumbed down if you don't mind indulging my crap inner mechanic) otherwise I'm going to be on foot for a while.