Is your LAN connection via a router? If it is, check that DHCP is enabled. If it is then there might be an option to see all connected devices. You can get their IP address from this screen.
If this option is not present then click Start >> Run and type in cmd and hit Enter.
In the command prompt type in IPConfig andh it enter. Look for IP address or IPv4 address.
Do this on each pc and note their IP addresses.
If you're NOT using a router and just a switch you're going to have to manually setup static IP addresses in the same subnet so they're on the same network. I won't go into detail unless you need help on that.
Your problem seems like Comp3 has is on a different subnet or permissions aren't properly assigned to the shared folder. I suspect its the former though.
They are connected via a router. DHCP is also enabled. Their subnet are also same ie. 255.255.255.0 How can i check the permissions – KoolKabin – 2010-11-30T08:20:22.087
I assume all the IP addresses have the same first 3 set of numbers given that subnet mask. You can check the folder permissions by right clicking on the folder and go to Sharing and Security. Under the Sharing tab your folder should be shared. Click on the Permissions button. Ensure that 'Everyone' is listed in the 'Group or usernames:' and that the 'Read' permissions in the list box at the bottom is checked.
Oh and on the Sharing tab make sure the 'User Limit' is set to 'Maximum Allowed' just to test. After it works you can set it to whatever you want. – QuiXilver – 2010-11-30T11:06:14.300