hangs on "starting kernel "

when the u-boot tried to boot the kernel, it hung on 'staring kernel' as
shown in the attachment, how can I go back to the u-boot prompt where I can
type u-boot commands?

upon booting,  I tried to stop autoboot by hitting keys, however it didn't
respond at all, I also tried ctrl+c, it failed either. How can I stop
autoboot and go directly into the u-boot command prompt?

Something looks unfamiliar here.  What is the USB message at the top for? 
Are you using usbpush?

It might help to state which u-boot and which kernel image.

Thanks for the reply problem solved.

It might be helpful to others to know how the problem was solved, IF the
solution is not embarrassing!