uboot启动后键盘无法输入任何命令该怎么办？

问题：
1、启动起来（ttl连接）会在第4行（config u***..）停顿一下，然后就直接到最后一行了（中间内容一闪就打印完了），没有选择时间
2、完全启动后，键盘无法输入任何命令？
下面是启动的前部分过程。

U-Boot 1.1.3 (May  4 2013 - 16:04:53)

Board: Ralink APSoC DRAM:  64 MB
relocate_code Pointer at: 83fac000
config u***..

Set info->start[0]=BF000000
flash id 0x227e, sector count 128, size 0x800000
flash_protect ON: from 0xBF000000 to 0xBF01F6CF
flash_protect ON: from 0xBF030000 to 0xBF030FFF
*** Warning - bad CRC, using default environment

============================================
Ralink UBoot Version: 3.5.2.0
--------------------------------------------
ASIC 3052_MP2 (Port5<->None)
DRAM component: 256 Mbits SDR
DRAM bus: 32 bit
Total memory: 64 MBytes
Flash component: NOR Flash
Date:May  4 2013  time:16:04:53
============================================
icache: sets:256, ways:4, linesz:32 ,total:32768
dcache: sets:128, ways:4, linesz:32 ,total:16384

##### The CPU freq = 384 MHZ ####

SDRAM bus set to 32 bit
estimate memory size =64 Mbytes

Please choose the operation:
   1: Load system code to SDRAM via TFTP.
   2: Load system code then write to Flash via TFTP.
   3: Boot system code via Flash (default).
   4: Entr boot command line interface.
   7: Load Boot Loader code then write to Flash via Serial.
   9: Load Boot Loader code then write to Flash via TFTP.

You choosed

0

3: System Boot system code via Flash.
## Booting image at bf050000 ...
   Image Name:   Linux Kernel Image
   Created:      2013-10-24  14:14:45 UTC
   Image Type:   MIPS Linux Kernel Image (lzma compressed)
   Data Size:    7255009 Bytes =  6.9 MB
   Load Address: 80000000
   Entry Point:  803b8000
   Verifying Checksum ...