You quoted that the ps3 has been in you DMZ for a Long Time. Have you tried checking the ip address the ps3 is getting and if it matches what is in the router also it might be worth trying to clear the Router log of who is connected as it does jam it up if devices are connecting. ie new laptops computers and equipment.
This sounds to me like a DNS issue.
In your PS3 web browser, type in the following: http://188.8.131.52
If the page load then the issue is with your default DNS. In this case, set up your PS3's networking with an advanced configuration and leave everything as automatic except the DNS setting. Set your primary DNS to: 184.108.40.206 and Secondary to 220.127.116.11 (This is Google's public DNS service).
Let us know how you go.