Do you think it could be a security or fuel pump issue or something else?

I was driving my 98 Linc. Navigator when it sputtered and stalled. After trying repeatedly to start it I noticed that the security light kept flashing quickly. I sprayed starting fluid into the intake and it started right up so I thought it might be the fuel pump but a mechanic I talked to thought that maybe the ignition key lost its code. I took the key to a hardware store where they read the key and said the code was still there so I had them transfer it to a new key but it fails to start the truck as well. I also noticed a very fast clicking sound coming from the fuse box under the hood that wasn't there before. Do you think it could be a security or fuel pump issue or something else?

Thanks,

Dale