Hi,
Maybe you have enabled client isolation? This prevents connected clients from being able to reach each other on the wifi.
For security reasons this is what you want. If not, then you can simply disable it in the WLAN configuration.
Also bear in mind that many operating systems (like windows) block ICMP Ping by default nowadays.. so it could be that your windows PC is not pingable anyway unless you enable ICMP PING in the windows firewall.
Best regards,
Bas Sanders