Can't connect to pc

I have a Samsung Galaxy Ace 4 Lte running android 4.4.2 and a PC running windows 8.1.

For a while now I haven't been able to send files to my device. My PC sometimes looks like it recongnized a USB device connected but then nothing happens (I was able to exchange files between them once before, but now it's impossible). I have tried changing cables (cables work with other devices except mine), I've tried other PCs, but the same thing happens.

Does anyone know what might be the problem?