have unstable working condition with DVI and USB Host

Hi,
I have just experiemented unstable working condition of DVI and USB. I use the image built by bitbake console-image.
At the beginning they were working fine. I can boot to the Angstrom Screen on DVI and I can use KeyBoard through the USB Hub. But after restarting for 5 or 6 times, I cannot use the Keyboard anymore. On LCD I can only the boot screen at the u_boot stage but I cannot see the Angstrom login screen. What I only have is the Terminial login on Minicom.
Could you please tell me what happen?

Best regards,
Thang Nguyen