My hard drive being extremely slow. I have just upgraded my hard drive from a 160 to a 500 gb

Question

I have just upgraded my hard drive from a 160 to a 500 gb drive. The only problem is it takes an eternity to load up anything from the drive. What can I do to verify that the drive is working as it should? It has gotten to the point where i have to wait 5 secs for a window to open.. Should I think about returning the unit back to the seller or what?