Unable to Access Any Other Computer in Workgroup or Homegroup

Hi I have a home network of 4 computers. I have recently installed Windows 7 on 3 of them - the other is XP Professional. Since then I have not been able to see/share/ping with any of the computers, which are all in the same workgroup. Also If i try to set up a Homegroup on the 3 Windows 7 pcs after creating a homegroup then trying to join it on a 2nd pc the message There is currently no homegroup on the network is displayed. My knowledge of networking is small. The networking Trouble Shooter gives a 'Your computer appears to be correctly configured but the DNS Server is not responding'. The Homegroup troubleshooter cannot find a problem on either machine. I have no problems connecting to the Internet from any machine. Any help would be greatfully appreciated.

Hi Roderunner, Thanks for the prompt response. Not sure what you mean by 'Network' Method. The network set up where I am having the problems is wireless (WAG 160N Router).

I have also connected 2 pcs via a LAN connection with not much more luck as follows:

Windows 7 pc and Windows 7 pc.
Could see and explore both PCs
Could not join homegroup on second machine. Trouble shooter on both machines failed to find a problem!

Windows 7 pc and XP pc.
Could not see or ping either machine!

Hi BillyAsh,

If you have any Firewall or Security Software installed on those machines, pls. disable them for now.
If you're using the Windows built-in Firewall, make sure that Files and Printer sharing is Excluded.

Create Identical UserNames and Passwords on both computers.

Please compare your current configuration on how to share files and printer.
Share Files and Printers between Windows 7 and XP - How-To Geek

Disable Password Protected Sharing in Windows 7:
Disable Password Protected Sharing — MAXIMUMpcguides – Windows 7 tips, tricks, help, and how-to guides

Verify that you are sharing the folder to Everyone, give full access for now. Were you trying to share the entire C Drive or subfolders in the C Drive? Please share the entire C drive for now, call it C.
Click on Start, type the \\ComputerName\C or \\IPAddress\C - The Computer Name or IP Address of the computer that you're trying to access in your home network.

Please post an update and let us know the outcome.

Hi Roderunner,
Tried changes in link you sent - no change to anything reportes above! But thanks for trying.

Hey 2xg,

Thanks for offering some advice. I went through steps you pointed out and in the links you sent. Exactly the same results except can now joing homegroup. So to recap:

Wireless:
No machine can see any other machine.

LAN

Windows 7 cannot see XP and vice versa.
Windows 7 machines can see and explore each.
Windows 7 machines can homegroup.

It's a start, thanks