Try testing the external drive on another PC if you can to see if this
slow data rate is seen - no point delving into the OS / hardware if
it's the new drive that's at fault !

If the drive is a slim-line one ( i.e. uses a 2.5" laptop drive ) then
sometimes the USB port cannot supply enough power and it will default
to a slower speed unless extra is provided - often using a USB cable
with twin plugs on one end. The second plug goes into another USB port
and only has the power rails connected. This usually affects laptops
but I've seen desktops with front USB ports that do this.

Failing that, have you any other USB devices plugged in ? Depending on
how the ports are wired a USB 1.1 device can bring all ports down to
USB 1.1 - controllers cannot provide mixed speeds to connected ports.