Lost network & 651 error

Yesterday had a network that was setup which included 1 Win 7 laptop and a WinXP laptop on wifi, and a WinXP desktop ethernet connected computer and a Win7 desktop ethernet connected computer (this is my main).
Today have no access from the main Win7 computer to any of the 3 others. The 3 can see it, though.
The only one the main "sees" is the Win7 laptop (wifi). But it can't access it even though from the laptop end, it is set for access from anyone on the workgroup network.

Also, the connection on the ethernet connected main Win7 computer was not the way it was connected yesterday. Instead, today it was connected via a wifi dongle I keep on it for safety.
When I tried to add back the ethernet connection (Realtek card) I received a 651 error message. I was doing it through the Control panel network area. Started researching the problem.
Changed the rasppoe driver (after the trusted installer issue) and it didn't make any difference which one used (orig or new). Rebooted the modem/router, and disabled the wifi connection. The computer connected up with the ethernet connection just fine.
However, I still can't access the network of the other 3 (workgroup) via the ethernet or the wifi network connection.
Unless I manually disable the wifi connection the computer utilizes the wifi instead of the ethernet connection. That's a weak connection compared to the ethernet.
Ok, I think, but how can I reset the workgroup network for this computer? It would seem I would go back to how I originally did it but for some reason the network/share in control panel networking are not doing the job or I have forgotten something.
I have checked the properties of almost everything to see if something seemed odd. It all looked normal but the IPv6 said no internet access and I couldn't remember if this was the way it was before when everything worked. If that's part of the problem, how do I change it?
I would like the main computer to always use the ethernet connection. Do is simply keep the wifi disabled or not? Would that stop my workgroup network from being available?

FYI: I can't setup a home group between the two win7 computers but never could. Device manager shows all working. No new programs or changes were made yesterday to the main win7 computer but an update of the Oracle Virtual Box was put on the other win7 machine in the network but that seems a longshot for explaining this.

Having had it all working fine for months and suddenly over night it changes, has left me wondering where to begin setting it back up from the main win7 desktop (ethernet). Any direction help would be appreciated.

I solved my problem and perhaps the following info will help someone else. I am not sure where to post it so a moderator might know best.
In my case I checked all settings and they were correct, so I thought about what had been changed or added in the past 24 hours. I had updated Virtual Box on one of the networked machines. This new update (an improvement for sure) also adds a new network for use with the virtual box.
When I noticed this unidentified network, I disabled it and the original network I use for my 4 computers, came back on. This new unidentified network seems to get in front of or temporarily replace the original one. So, be aware that the improvement in the virtual box has to be tailored to your needs.