Cant copy files from PC to android phone

[AC Question]

I recently started getting the "this Device has either stopped working or has been disconnected" message whenever I try to transfer any file from my PC to my HTC One m8. It was working fine until a few days ago I haven't installed anything new on my phone or computer and can't figure this one out.

I'm running 6.0 marshmallow
Please help!

Things I tried so far:

Restating phone/computer
USB debugging on/off
Different USB cables