Can't open Mac OS X shared folders with Windows PC

I am replacing my Mac Pro (Snow Leopard) with a Mac Pro with Lion (OS 10.7.5) and my Windows PCs (Windows XP, Windows 7, Windows 8) are not able to connect to the shared folders on the newer Mac Pro.  They had no problem connecting to the older Mac Pro.  I have gone through all the steps and tried to keep things as simple as possible - everyone is on the "WORKGROUP" workgroup.  The 2 Mac users are simple-short names with simple passwords -- AND they work fine on the Mac.  There is no Firewall on any Windows PC.  Whenever I try to connect with the Windows PCs, I get the window that prompts me for a user and password.  No matter what combination I use, I can't get beyond that.  I have checked SMB on the Mac.

Is there a firewall I need to turn off on the Mac Pro?
Could this be related in any way to my AT&T router?
Years ago, I changed the IP range to 204.1.1.X.
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Eoin OSullivanConsultantCommented:
In relation to your questions
1. Is there a firewall I need to turn off on the Mac Pro?
There is a firewall on OSX Settings under Security and Privacy (check it is turned off for now)

2. Could this be related in any way to my AT&T router?
Probably not if all the other devices are working OK.

The steps to check on OSX in System Preferences under "Sharing" is to ensure that ...
File Sharing is turned on and under the OPTIONS that SMB is enabled
Then look at the 'Shared Folders' in the Sharing settings and see what folders are being shared and what users have Read & Write access ... if necessary change the permissions to Read & Write for whatever user you are using to connect if it is not showing properly.
Note the IP address of the Mac

On Windows
First check the connection by doing a ping to the IP of the Mac ... and ensure you're getting a response
Open a new connection using the IP address and not the name of the Mac    \\204.1.1.x\SHARED-FOLDERNAME

It is worth noting that apple changed the version of SMB on OSX 10.7 which is probably part of the issue you're having.
The new version of SMB was quite unstable at first .. especially connecting to older versions of Windows .. can you upgrade the newer MacPro to 10.8/10.9 and improve SMB?

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This problem is not likely caused by your chosen IP address scheme, but you should plan to change it at your earliest convenience, because it may cause strange problems over time. The 204.1.1.x range is in public IP address space, so it's possible you would have problems without much clue that is the cause.
There are plenty of good IP address ranges in the private IP space:

As security becomes more and more of a concern, the possibility exists some security software, or an appliance or even security-conscious apps may not recognize devices on your LAN as being local since they have public IPs. Who knows, why chance it?

Good luck--
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tcexperts77Author Commented:
Everyone has excellent comments.  
I am still stuck with this, but am planning to go to Mavericks or back to Snow Leopard:

To Roshan Ejaz:  I installed SMBbUP and it gives me an error that it can't start.
To eoinosullivan: I've done everything you suggested with no success.  
Is SMB better in Mavericks?
To schaps: I will change IP range later for security (not now, since it worked fine when I had Snow Leopard). Thanks
Upgrade to mavericks and we will take it from there as no point fixing it now to have a different issue or no issue in Mavericks.
Eoin OSullivanConsultantCommented:
Move to Mavericks first as SMB is better and you'll get the benefit of that.  Then retry connecting from windows.
Unless you have previously downloaded the Mavericks upgrade file, you will now only be able to upgrade to Yosemite. Just FYI.
tcexperts77Author Commented:
Fortunately I helped a friend download an upgrade to Mavericks about 2 weeks ago.
The download was deleted, but I just retrieved it by signing on the App Store with his ID.
I will upgrade to Mavericks tomorrow.
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