Sounds like the power button and the volume button were pressed at the same time forcing it into download mode. You may need to reinstall the firmware using odin to recover it.
Phones & Tablets: Galaxy S4, Galaxy Note 8", Evo 4g LTE, Evo 3D, Acer Iconia A500, Samsung Galaxy Tab 2 10.1, Ipad 2, Nabi 2,
Rom: Rooted Stock for now, Hotspot Mod, Xposed, Wanum
Kernel: Stock for now