From your answer to another post that you are using a Workgroup, the most likely problems are that the user/pswd are different or don't exist on the server, or the user/pswd is not being passed in the correct syntax. In a Workgroup Users are local to each machine, JSmith on the server is not the same as JSmith on the workstation.
A Domain solves both of these issues and has many other advantages if you have more than 4-5 workstations. This is the best solution.
Option 2 is to setup a username and pswd on the server. This can be 1 server user for each wkstn user, 1 server user for each user security group desired: Accounting, Sales, Marketing, etc, or 1 server user for all users. The server username & pswd may, but are not required, to match the username and pswd on the wkstns. Don't use any blank passwords.
Create a batch file on each machine to map the shares as a drive letter and force authentication on the server. Place the batch file in a C:\Admin folder, place a shortcut to the batch file in the All Users Startup folder to have it run on logon, set it to run minimized. The syntax is:
"Net Use X: \Server\Share /User:Server\User Password".
"Net Use /help" will provide more examples.
Net Use X: /del will remove the drive mapping for testing, it will not delete any data.
You can also test authentication against the server with the Net Use command. If the authentication fails with "incorrect user name or password" then either the syntax, username, password or some combination of all 3 are wrong.
Option #2 is not secure and not recommended but could work as a temporary solution.
Best Answer
There are a lot of ports required for the successful functioning of Windows file sharing. You need at least these ... and heck, there may be a couple I've forgotten:
Start with trying to telnet to those TCP ports. If you get a "connection failed" type of message, then you know with certainty that there is a firewall (hardware or Windows firewall) in the way between you and the share... Assuming of course that file sharing is set up and working correctly from within the datacenter.