Every so often I lose the ability to upload files to my web server through any means at all: Filezilla, Fling or via my web host's log in screen.

When I restart my PC it all works fine again for a while but eventually it stops again till I restart again. My system specs are below.

I've tried turning off my Avast antivirus and Windows firewall but neither makes a difference, only a reboot helps.

Any suggestions as to what may be causing this? I recollect the problem started a few weeks ago.

Operating System: Windows 8.1 64-bit (6.3, Build 9600) (9600.winblue_gdr.131030-1505)
Language: English (Regional Setting: English)
System Manufacturer: TOSHIBA
System Model: Satellite L875D
BIOS: 6.10
Processor: AMD A6-4400M APU with Radeon(tm) HD Graphics (2 CPUs), ~2.7GHz
Memory: 16384MB RAM
Available OS Memory: 15836MB RAM
Page File: 3383MB used, 14885MB available
Windows Dir: C:\WINDOWS
DirectX Version: DirectX 11
DX Setup Parameters: Not found
User DPI Setting: 96 DPI (100 percent)
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Disabled
DxDiag Version: 6.03.9600.16384 64bit Unicode