win7下无法ping通开发板

通过sd卡启动光盘自带的uboot之后，使用uboot菜单中的测试网络，能够测试成功，提示：
#####    Boot for TQ3358 Main Menu      #####
#####     EmbedSky TFTP download mode     #####

[1] Download u-boot.bin to Nand Flash
[2] Download MLO to Nand Flash
[3] Download Linux Kernel (uImage.bin) to Nand Flash
[4] Download LOGO Picture (logo.bin) to Nand  Flash
[5] Download UBIFS image (root.bin) to Nand Flash
[6] Download YAFFS image (root.bin) to Nand Flash
[7] Download Program to SDRAM and Run it
[8] Boot the system
[9] Format the Nand Flash
[0] Set the boot parameters
[a] Download User Program
[n] Set TFTP parameters(PC IP,TQ3358 IP,Mask IP...)
[p] Test network (TQ3358 Ping PC's IP)
[f] tftp uboot.bin to SDRAM and Run it
[r] Reboot u-boot
[t] Test kernel Image (uImage)
[q] Return main Menu
Enter your selection: p
TQ3358 ping PC IP:ping 192.168.1.138
link up on port 0, speed 100, full duplex
Using cpsw device
host 192.168.1.138 is alive
看提示是测试成功，但是使用tftp命令下载文件到开发板时总是不成功，再在win7下ping开发板无法连续ping通，要不就是超时，要不就是无法ping通，请问是怎么回事？
开发板通过直通线连交换机，笔记本也是通过直通线连到交换机，照理是不是不应该发生这种事儿呢？

tftp是不太稳定，用SD烧写比较好

我也这样的情况，ping不通