Can't access win8-win7

Hi all,
I'm going nuts!! hoping anyone can help

My home environment includes
1. my own laptop win 8.1 enterprise (no GPO, no domain, just a standalone)
2. media PC- win 7 ultimate
3. my GF's laptop - win 7 ultimate

i used to access the media PC using a cable towards a share on top of it.. funny thing is, i bought a TP-LINK wireless dongle the other day and since than i can't access the share or even ping my w8 and the pc (w7) in both ways! using the IP address of the dongle (disconnected the cable). when i reconnect the cable and disconnect the dongle, everything's back to normal
I'm aware of course to the IP changes between the interfaces..

I don't see how much of even a ping can't get through anymore (both ways). firewalls are down on all machines and on all environments (guest, local etc.)
my other laptop works fine with the pc (win7-win7)

network discovery is on all environments on all machines, changed "disabled require 128 encryption" and "Set to Send LM & NTLM responses only" on both machine


I would really love your help here

thanks a bunch!