Can not be booted
 

Why can not my computer be booted with a bootable disk?the bootable disk is created by me,the Windows iso is downloaded from Microsoft website,Google tells me it's the right thing to do,i don't know what I did wrong, bootable Windows disk?

Did you go into set up as it boots and select the drive or USB stick to boot from as it may still have the main drive selected, so simply ignores your boot disc and tries from your normal drive.

You will need to ensure that the DVD drive is either designated as first in the boot sequence (followed by the Windows boot Partition /Drive) or use a startup menu (varies by System) to select it to boot from DVD on this /the next occasion.
A bootable windows 8 or 10 disk will contain the correct security files /EFI folder or partition for Secure boot that a bootable programme disk must have for most modern BIOS'es to load/run it. (If not {e.g. early windows 7} change BIOS settings to temporarily choose No in Secure Boot section or Compatability mode in Boot settings
If that all fails copy the entire windows disk including any hidden partitions to a USB drive and see if you have better luck that way. With a valid licence you can download a bootable USB stick or make a DVD iso file on the windows support website.

I did set USB as the first boot device on biso menu.but my computer still hasn't been booted.

I made a bootable USB disk and used it to boot computer,this is the first time I've done this, and I've been very careful,i don't know what i did wrong,and i have tried it on another computer,i got the same thing.
Maybe I'd better do it all over again.

There are some video instructions on YouTube for making bootable Windows USB,or click here that you can follow them.