If iTunes also cannot find a connection, looks like these programs are being blocked by something, most likely a firewall.
With your Windows Firewall, may I suggest you create sub-rules for these programs, allowing all ports access for each of UDP & TCP. With Windows Firewall you can create a sub-rule for each of TCP & UDP. Just adding a program alone might only add clearance for TCP. In the Firewall Exceptions tab, select LW, choose Add Port, then add UDP & a wide port range.

I cannot find Dynex DX-D402 listed anywhere, even at the Dynex site. Did they sell this part of their business to another company because they no longer have modems listed as present products? I did find DX-E402 listed at portforward.com.

Problem might be the Dynex router's NAT which acts like a firewall. You can try port forwarding the device to allow ports for LW to access through. Two main steps to achieve this. The first being important to do first.

1. Setting up Static ip address on Vista

2. Port forward the Dynex DX-E402. Unfortunately in the first step they show they use a LW 4 sample image. Instead see Manual port forward instructions & sample image for LW 5 sample image. Port LW uses for both connecting & listening need to be identical to the port(s) port forwarded.

Note: If you have issues logging into the device as on those instructions, try ip log-in address http://192.168.2.1 and if their instructions for log-in page do not work, then leave the password blank and click Submit.

After doing this you should save settings, reboot modem (generally done by unplugging power for a minute.) And also reboot computer.