Connecting External HDD to Network

This isnt so much a problem more than i have no idea how im going to do it.

I have 1 PC and 3 Laptops plus a Xbox. All the laptops and my PC are wireless the xbox is wired directly to the Router. my external drive is connected to my PC, but i want to be able to access it WITHOUT my pc being on. I was thinking that if i connected it directly to my router that it would be the best solution. but i have no idea how i would do that., It's a USB 500GB external, and i have a 4 port wireless Router. Any hints?

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