求助，U盘挂载不成功

MICRO2440  使用光盘自带的映像文件 按照用户手册进行LINUX系统安装 进入系统之后无法加载U盘，但SD卡可以。
确认U盘格式 FAT  和FAT32 都试过 先后换了四个U盘 效果一样，
后来改成WINCE系统 一插上U盘就死机。
在LINUX系统下 用串口终端输入 fdisk -l等命令 提示not found
这是什么问题呢？头都大了

信息太少

[root@FriendlyARM /bin]# usb 1-1.2: USB disconnect, address 5
usb 1-1.2: new full speed USB device using s3c2410-ohci and address 6
usb 1-1.2: New USB device found, idVendor=17ef, idProduct=3818
usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-1.2: Product: USB Flash Drive
usb 1-1.2: Manufacturer: Lenovo
usb 1-1.2: SerialNumber: AA08102400006296
usb 1-1.2: configuration #1 chosen from 1 choice
scsi2 : SCSI emulation for USB Mass Storage devices
scsi 2:0:0:0: Direct-Access     Lenovo   USB Flash Drive  1100 PQ: 0 ANSI: 0 CCS

sd 2:0:0:0: Attached scsi generic sg0 type 0
sd 2:0:0:0: [sda] 3915776 512-byte logical blocks: (2.00 GB/1.86 GiB)
sd 2:0:0:0: [sda] Write Protect is off
sd 2:0:0:0: [sda] Assuming drive cache: write through
sd 2:0:0:0: [sda] Assuming drive cache: write through
sda: sda4
sd 2:0:0:0: [sda] Assuming drive cache: write through
sd 2:0:0:0: [sda] Attached SCSI removable disk

mknod  /dev/sda4 b 8 4
mount  /dev/sda4  /mnt

mark一下，自己的也有问题！