That message is usual for most pc`s if you plug something in front usb ports because they are connected to last controller in the motherboard. Of course that depends from mobo to mobo by their hardware difference. Even if you have only 2 usb ports in the front only one of them should be r.1 which cause that message (and low speeds) if you plug something native r2 in it. If they are 4 in most old mobos 2 are r.1 and 2 - r.2 and for new motherboards that number is 3 r.2 and 1 r.1. But that too can depend from the way of connecting.
With r.1 I allude to the old standard usb 1 which is super slow. With r.2 I allude to usb 2 standard which is normal nowadays. There are new r.3 - usb3 format which is super fast but he will be implemented everywhere from now on.
So. Did you try to use the usb ports that are placed directly on the motherboard? They all should be default usb2.
And if you use one of them did you try the other ones?
Also you skipped to say what type is your external harddrive.
Because 3.5"ones come with ac/dc adapter to manage needs of voltage.
2.5"ones which use only usb port, sometmes have 2 jacks to can suck enough voltage to work. And if your is that type then did you check if your PSU give enough power to empower it for stable work?
English is not my native language so I struggle to find and use correct words. So if you can`t understand something ask me without worry