Can't ping other machines in my network

Either your wireless AP or your clients have a bug in how they're handling the WPA2-PSK group (multicast/broadcast) keys. Because of this, ARP broadcasts aren't getting through from one client to another. Without ARP, they can't learn each others' wireless MAC addresses, so they can't address the 802.11-layer headers of the ping frames.

Enter static ARP mappings between two machines and see if they can ping each other -- I'll bet they can.

If you enabled WPA2 "mixed mode", where both WPA[1]-style TKIP and WPA2-style AES-CCMP are both enabled, see if your problem goes away when you switch to pure WPA2 (AES-CCMP only). Hopefully you don't have any TKIP-only clients that this excludes. Mixed mode is a little tricker than pure WPA[1] or pure WPA2, because it requires a TKIP group key but AES-CCMP pairwise (per-client unicast) keys.

Make sure your AP's firmware and your client machines' OS, wireless software, and wireless drivers are full up to date, in case your vendors have fixed their bugs.

Make sure to buy Wi-Fi certified equipment. Look for the Wi-Fi certification logo. This is why the Wi-Fi Alliance exists, to make sure that 802.11-based products follow the specs correctly and interoperate properly.

i would rather check the firewall of your windows7-machines.

follow this to allow windows7 to react on icmp-packets.

(it is unlikely the router will block icmp-packets from the lan to the lan).

This pointed me in the right direction. Switching the router from WPA-2 to WPA+WPA2 allowed my windows 7 machines to ping each other and the home network to function again.

It broke when I received a new modem/router from my ISP so I imagine the issue is with the router, rather than the windows machines.