Help! USB portals not working!

Hi,

I'm in need of some help, last night I was using my external hard drive and in a rush I didn't safely eject it from my Mac Book Air and now my USB portals aren't registering y external hard drive or USB's. I've checked the hard drive on another computer and all my work is still on there but my computer just isn't registering that it's plugged in to either portals. I've checked in my preference and de-selected and re-selected the external and USB boxes but it's done nothing.

What do I do?

Thank you!!!!