Windows 10 does not boot when I remove the old HDD?
You either need to move the ssd sata plug to where the old HDD plug was or in the Bios make the new ssd the top of the boot order. Another problem people sometimes have when installing a fresh installation over doing a clone of the old hard drive is that they don't remove the old drive so that the boot sector for the new install gets put on the old drive even though the install gets put on the new drive. If you simply cloned, your problem is that your computer is still pointed at your old drive as the boot drive, simply reassign the new drive in your bios as the boot drive.
Jiraiya The Gallant
Should reformat, reinstall Windows on the SSD Should only have the SSD connected during the Windows setup, as well. Can format the hard drive too.
Your boot menu is on the old hard drive so you need it to be able to boot Windows. What you should have done was remove the old hard drive then install Windows on the SSD. The boot manager would have been on the SSD then.
the drivers for your mobo need to be installed and accessible or windows can't start. are those drivers on the SSD? if not, the machine won't start because it can't find the hardware