Solution? same problem. the bug start in windows server 2012 R2. i'm using same programs.
I am using SQL server 2014.
The xampp version i am using is 1.6.8.
Tried this also with 5 different websites from the public archive.
Already opened ports 80 and 1433 and made sure no other application was using them.
Enabled all protocols in sql server configuration manager
Tried turning firewall off and it didn't work as wel.
Reinstalled xampp and tried different versions but it didn't work.
In the .\SQLEXPRESS host, i also tried adding ,1433 and it didn't work