Ext hard drive problem?

Hi guys.I’ve jast bouth external hard drive,it seems to work ok,butt when i restart my computer it freezes at the boot screen.I have to turn it off and on several times before it starts.Could it be usb port problem?

I’ve just built a new PC & it does exactly the same with a USB external plugged in/switched on. I just make sure it’s not on/connected when I boot the system.

So i have to disconnect it every time i restart my computer?Oh one more thing,ipod does the same thing.Is there any way to fix this?