How to access MS SQL Server database from other computer connected in workgroup?

How to access MS SQL Server database from other computer connected in
workgroup?

I have made a C# application which uses SQL server database. I have other
computers connected to me and to each other in workgroup. I have shared my
C# application with others. When they open the application they get the
error "A network related or instance-specific error occured while
establishing a connection to SQL Server. the server was not found or was
not accessible".
But the application is working fine on my PC. The connection string I am
using is
"Data Source=ASHISHPC1\SQLEXPRESS;Initial Catalog=ACW;User
ID=ash159;Password=ashish159" which is stored in a CONFIG file.
The application is working fine on my PC. What must I do? I have enabled
the TCP/IP in the server but the same error persists. Some change in
connection string or something else?
Please help.. Thank you..