iMac not recognizing external drives

[Arizenheimer]

A couple days ago I noticed that I couldn't get my phone to mount on my iMac. As I was trying to figure out what was going on I tried hooking up a flash drive and another external drive that I have into the USB ports and am seeing nothing on all of them. I know that my drives work as I've used them recently on other computers.

I've got a couple of external drives that I always have hooked up as media drives. I tried ejecting those to see if I could use those ports for one of the other drives I was having problems with and of course now the iMac doesn't want to recognize these either. So now I'm in real trouble. I've tried restarting and can only get it to recognize the external I use for backup & one of my media drives. Can someone please help me. I'm really starting to freak out here :-/