8168 evm boot from nand problem

u-boot: ti-ezsdk_dm816x-evm_5_03_00_09/board-support/prebuilt-images/u-boot.noxip.bin

I download the u-boot from pc to nand flash 
TI8168_EVM# mw.b 0x81000000 0xFF 0x260000 
TI8168_EVM# tftp 0x81000000 u-boot.noxip.bin 
TI8168_EVM# nand erase 0x0 0x260000    
TI8168_EVM# nandecc hw 2 
TI8168_EVM# nand write.i 0x81000000 0x0 0x260000 
TI8168_EVM# nandecc hw 0

sw3[4:0]:10010
sw4:nand on

power off, power on the EVM board, and nothing is out put form the serial port

what's wrong with me, can somebody help me?Thanks