PCs on home network suddenly can't connect to iMac

My iMac is reading our Windows XP and Windows Vista PCs on our home wireless network fine, and up until yesterday, the two Windows PCs were reading my iMac perfectly.

Today the two Windows PCs won't accept the usual username/password combination to read the iMac.

The Connect to.. window with 'Incorrect password or unknown username for \\MYNAMES-IMAC\myusername\[rest of path]' opens, but the username box shows MYNAME\myusername. I've tried entering the password with this username and I've tried changing the username to MYNAMES-IMAC\myusername and just the username on its own but this doesn't work either.

I haven't changed any firewall settings or passwords since yesterday!!! How do I get them to reconnect?

I'm sure the Windows XP PC doesn't ask me to enter the password every time I reconnect to it (ie every day). The Vista one does. But when they did, they always accepted the password. Reconnect on startup is enabled. I can't even remap the iMac drive as the password isn't accepted! Grrrrr.....

Any ideas gratefully received.

iMac and network problem

Hi,

I have exactly the same problem but mine appears to have started since upgrading to mountain lion. The iMac appears on the pc but won't accept the logon. I also have the problem with File Browser on the iPad. That too won't logon to the iMac..

Any help on this would be much appreciated