Samsung Galaxy S3 won't boot.

[mablibsking]

So my G3 was a rooted phone, and today as I plugged my phone into the computer, Samsung Kies wanted to update, and I clicked yes, not knowing better. Then it did the whole updating thing, and it didn't work. So, being curious, I went on the phone using the system update there, got the update to work, and it installed, and asked to reboot. I clicked yes. The problem happens. It doesn't reboot, it only shut down. I can't get it to boot again. When I boot with the power button, it goes on, then it goes off right as the words "Samsung" come on. It also has the words "Recovery Booting" On the top left side, but that including the Samsung logo disappeared in a second and its back to black powered down screen. Does anyone know how to fix this? Thanks!