Do you still have warranty?
I have similar problem with my G300. I'm on Electra ROM but don't think that matters.
Turning phone on just displays splash screen.
Power on with Vol+ just displays splash screen.
Power on with Vol- just displays splash screen.
Power on with Vol+/Vol- goes to update but update never finishes.
The only way I've been able to get to phone to boot is to remove the battery then connect to USB power. Splash screen displays. I put battery mostly back in but just touch the battery off the spring contacts a few times ( effectively bouncing the battery off the contacts a few times ) The phone will reboot to splash screen usually but sometimes it reboots normally. I may have to try several times but eventually goes past the splash screen and reboots and I gain access to my phone again.
I've tried clearing everything possible once getting access again but this still happens when I try to reboot phone ( not always but most times ). But so far I've been able to re-gain access doing it this way...not ideal but only solution I've been able to come up with.....
Might be worth a try for anyone stuck on splash screen....let me know if it works for anyone.....
Have you tried this with the battery removed?