I bought a Lacie mobile hard disk with a capacity of1.5tb. The partition can be seen in the disk management. But I didn't show the drive letter on my computer. Solve.

Hello, landlord.

The newly bought hard disk should be able to rule out the cause of the hard disk itself. Please check whether there is a "Universal Serial Bus Controller" option in the Device Manager. If you don't have this option, please set the USB control to enabled in "Chipset Function Settings" or "Integrated Peripheral" of the BIOS, save and restart the computer.