Windows 7 clients can no longer access network drive

My Windows 7 Pro x64 computer (computer #1) can no longer see my shared network drive that is attached to my Asus RT-N16 router that is running its Samba server. I have checked that the workgroup is set to WORKGROUP on both the server (in the router) and on my Win7 client system. I was able to access the shared drive just fine a few days ago.

I have a Raspberry Pi on the network that is still able to access the shared network drive just fine. This would seem to indicate the Samba server in the router is still working. So I started up another old Win7 computer (computer #2) on the network. It is also unable to see the shared network drive, although it is able to see Computer #1 on the network. And Computer #1 was able to see Computer #2 when it booted up.

I have tried rebooting the router. I have not made any changes in the router configuration in the last week. I'm stumped. Any suggestions on what else I should check?

You are the 2nd person with a similar problem in the last 2 days, see http://www.sevenforums.com/network-...-visible-xp-machines-within-same-network.html

You: Win7 machines see each other but not the others, while others see each other but not the Win7.
The other person: Win7 machines see each other, XP see each other but neither XP nor Win7 see the other OS.

I wonder if you guys have anything in common. Like a similar security software? Which one do you use?

On Computer #1 I run Microsoft Security Essentials and also MalwareBytes. On Computer #2 I just run Microsoft Security essentials.

Additional data: Computer #2 is a lab computer that is set up to dual boot to Windows 7 or Linux Mint. When I boot it into Linux Mint, it can see the shared network drive, Computer #1, Computer #2 and the Raspberry Pi. But when I start it running Windows 7, in the Windows Explorer / File Manager / Computer application, in the Network section, it only sees Computer #1 and itself (Computer #2). Similarly Computer #1 can only see itself (Computer #1) and Computer #2.

The computers and network drive are all in WORKGROUP and they were all working fine a couple of days ago. I can't figure out what could have changed, nor where to continue troubleshooting.

So I started a couple of old laptops on my LAN to try and troubleshoot why I can't see my network drive from my Windows computers. The windows laptop #1 also can only see the other windows computers on the LAN, not the Linux computers or the shared network drive. But the Linux laptop can see all the Windows computers, plus the Linux computer, Raspberry Pi and the shared network drive.

So I went back to computer #1 (Windows) and tried mapping the shared network drive directly. It was able to map the network drive and access it. So in Windows Explorer file manager, the network drive is now mapped as drive M: and it shows up in the "Computer" section, but still does not show up in the "Network" section.

So what could happen to prevent the Windows computers from being able to scan the network and see the Linux shares, even though the Linux computers can still see both the Windows and Linux shares? I am puzzled, but at least now I can access my network drive again in order to move files there.