my 1998 GMC z71 cranks but will not start

I'm not sure if I'm supposed to but there is a black box a black plastic box underneath the dash that's plugged in that controls your security I forget what its called but when you open up It has a computer chip in it and I'm not sure what it is but I unplugged it and it made my security light go out but it still won't allow it to start so I plugged it back in in the security light came right back on so Could that Be my problem?

I've done once you put a brand new fuel pump distributor cap and rotor plugs wires all new sensors and it has a half tank of fuel the internet 60 pounds of pressure well it varies from 60 to 65 pounds of pressure of on my fuel line so I'm really not sure what the problem is the only thing that I haven't replaced yet is the fuel filter but I don't see why that would leave the security light on I hooked up my computer tester I have a high dollar computer tester I cannot remember the name of it right now but I ended up paying like $500 for it so I hooked it up to my truck and I went to go read diagnostic codes and it keeps coming up crankshaft position sensor I think the code is P0399 but it keeps coming up crankshaft position sensor I'm not sure what code number it is I'm just taking a guess I'm at but that keeps coming up so I erased it and did it again but the weird thing is I replaced every sensor under the hood and on that motor the crankshaft position sensor is brand new but my other question is I have a really bad oil leak and I'm going to fix it once I can get it running again so I can move it into the garage cuz its in the yard right now and there's oil all over my connector from the connector itself to the crankshaft position sensor so what I have to clean that up with some brake cleaner because maybe it's not supposed to have oil there and clean out the crankshaft position sensor because I noticed the crankshaft position sensor isn't tight it moves around me a twin allows oil to pass through it but its brand new so I don't think that should be a problem should it?

sorry about any typos mess ups I'm using talk text through this whole thing I hate texting lol

and the weird thing is even with the security light on it will fire off of ether aka starting fluid so I'm not sure on that one either this truck is very confusing this is my mud truck but if I cannot get it straightened out seems have this is my only truck at the moment I'm going to have to convert it back to carburetor so if y'all could help me out that would be greatly appreciated