This is the most common problem that I encounter when we make a home network using Windows Workgroup that Windows starts asking for username and password when we try to access a shared folder across the network. The worst condition comes in when Windows asks for only the password. The user name is defaulted to ComputerName\Guest and the field is disabled. I have never been able to logon using ANY password under this situation.
Go to Start –> Run –> compmgmt.msc
From the left hand pane, select Local Users And Groups –> Users
In the right hand pane, right click Guest and go to properties.
Check “Account is disabled” option.