- If you are using static IP on the DNS (not DHCP) then you should verify that the router did not give the same IP address to some other box. Usually you can configure the range of IP addresses that the router provides via DHCP. Make sure that your static address is outside of that range. If you change DHCP settings on your router you should restart the router and then restart all the machines on the network, so they get their new addresses.
- Assuming that your IP addresses are OK (which is quite possible since you seem to have no trouble accessing the DNS from your PS3 / Macbook), this is probably a Win7 issue. Antivirus program should not make any difference, but firewalls could. You should check the Windows Firewall settings...
- I think Win7 creates 'networks' not simply by IP range, but also taking the MAC address into account. So when you put in your new router Win7 recognized it as a new 'network' and asked you if it should be configured as 'home' or 'work' or 'internet'. This (I assume, I am NOT a Win7 expert) has to do with firewall settings. If you did NOT specify 'home' as network type, Win7 might simply not let you mount drives from the network. I am just guessing. See if you can check / change the network type.
- (Actually this 'network' thing is a feature, not a bug, in Win7. They probably let you specify both firewall and IP - DHCP vs. static - parameters by 'network', so if you move your laptop between home and work/school it will always recognize which network it is on and use the appropriate settings. But - like all new features - takes time for us, users, to figure, how to use / setup these things. And it is a bit confusing that when you replace your router it calls it a 'new network' even though for you is the same old, only with a new router.... Again, I am speculating.)