Engine is cranking but not starting

Within the past month, I have replaced the starter, the battery, the battery terminals, and the alternator. My car has been driving perfectly fine ever since. Then yesterday some neighbors asked me to jump their battery. Everything was hooked up correctly but when I went to start my car it would not turn over suddenly. Now it is cranking but not starting. It sounds like it is almost turning over but cannot. My security light is not blinking but I still tried leaving the key in the on position for periods of time on the off chance it was the security but it did nothing. Tried getting the battery jumped just in case but it did not do anything. I have no idea what to do anymore. Any ideas?