1. Check the eLog services, all of them run normally
2. Check the program installation in eLog server, found some unkown programs installed on the server
3. The communicate to eLog server still failed after uninstalling the illegal software above.
4. Check the security policy "Local Security Policy”-->“IP Security Policies on Local Computer" on eLog server, there is an policy to deny port 1433 which is the port of mysql database.
5. Change the database port from 1433 to 1133, login to eLog server successfully.
6. Confirm with customer that they didn't install any third-part software, it should be installed by hacker and the port 1433 was blocked by policy which created by the software.