Network / Sharing :: Computer Disappears From Local Network After Few Hours

I have a local network at home with 1 router, 5-6 computers and a few gadgets connected through WiFi.

I have a problem with one of the computers with Windows 8.1, let's call it Computer A. When I boot it, it is connectable from the other computers using its local IP address. But after a few hours it usually disappears from the network, and I'm only able to connect to it using the router's external IP and port forwarding.

By "disappears from the network", I mean that it's still connected to the router and to the internet, but none of the other units on the network is able to connect to it in any way.

Computer A can always connect to the the other computers on the network and to the internet.

The problem is solved if I reboot Computer A, so at the moment I have a scheduled task to reboot it every night. Unfortunately, sometimes it disappears from the local network after only a few hours after boot.

Turning the firewall off on Computer A doesn't work.

Below is the result of ipconfig /all on Computer A:

Code:
C:WINDOWSsystem32>ipconfig /allWindows IP Configuration
Host Name . . . . . . . . . . . . : bjarte-media2 Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Hybrid IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No DNS Suffix Search List. . . . . . : getinternet.noWireless LAN adapter Local Area Connection* 2: Media State . . . . . . . . . . . : Media disconnected

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