Hi all I have a very annoying problem

I have 4 computers connected to a router which is like a RTA300 dynalink or sumthing... and the network used to work fine, all of my computers used to connect to each other, then one day i did something and i cant remember what but i cant get onto the network at all ! I get the error message "Mshome is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access permissions. The list of servers for this workgroup is not currently avaliable" this is sooo annoying ... no matter what i do ... ive tried changing the workgroup name, my computer name, my comp description ect ive also fiddled round with the network settings ... im afraid if i tinker any more ill end up screwing everything up !
Plz help !