Immediate Shutoff topic

I'm not too sure what is happening here, but my phone has been acting all month. Sometimes it randomly shuts off on it own, afterwards i would just restart the phone, and it would work fine. Today it did the same thing, but now my phone won't reboot. it'll power up for about 2 seconds, and immediately shut off. For the most of the part Im thinking it might be a software issue, not my battery. Im running a Phoenix Rom from another galaxy s4 carrier with a patch to work with Verizon models. At this point I can't doing anything with my phone (enter recovery or download mode). Any help would be greatly appreciated..