It sounds like you have the wrong drivers installed on your PC.

Delete the old drivers via system devices and then plug the phone in and let it re-install the correct drivers.

or

Try installing WUGS nexus tool kit, Wugs has a driver install program that may help.

ALSO NOTE: That the old Samsung drivers for the Galaxy Nexus will work for the Nexus 5, odd but they do work for LG.

 

Have you ever thought about, or used, a cloud service? I've used Dropbox for years...I don't remember the last time I actually plugged my phone in to transfer anything.

If I want music on my phone, I put it in a Dropbox folder on my laptop and then download it from the same folder on my phone. Works like a charm.

Same thing for pics, movies, docs, ppt's, etc...

 

I had this on my old N5, new one is fine. Not the reason for the return.

Didn't have to do anything with drivers. I ended up using Airdroid, a bit slower but worked a treat.