The boot process looks for a partition with a flag indicating it is "active" or "bootable". A full disk copy should carry over this information, but maybe it got lost. While you still have a working Windows system, go to Disk Management, highlight the partition on the new drive with the OS, then mark the partition as Active.
Alternatively, from a USB stick, run a utility like Parted Magic, Partition Wizard, etc. to set the flag on the partition with the OS you want to boot.
Most modern motherboards have a bootmanager function available. Check the manual for the key to press early in the boot cycle. Usually F8, F12, or Esc. When the menu appears, highlight the device to boot. This overrides the boot device priority list set in the BIOS and will allow you to test booting from the copied drive before removing the original.
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