Upgraded To Linksys WRT54GL V1.1 Wireless Router Now No Internet Connection

2 routers (only one in use at a time!):

(A) Linksys BEFSR41 v3.1 Etherfast Cable/DSL Router w/ 4-Port Switch
(B) Linksys WRT54GL v1.1 Wireless-G Broadband Router w/ 4-Port Switch

Both routers are set to provide DHCP.DSL modem: Verizon Westell Wirespeed B90-210015-04 I have no idea whether this modem is also a router, but everything used to work. OS: Windows 7 Professional N x64, SP1 My computer has two ethernet ports, but only one is in use at a time. I also have VMWare Workstation installed, so there are a couple virtual adapters in the mix, but VMWare is not running during any of these tests.Yesterday (Sat, 10-Mar-2012) I replaced my old router (A) with the new one (B). The A router has been working fine for many years; I just needed wireless access. After the initial setup, the B router worked fine, using hard lines connected to the switch ports, and the wireless access features (laptop and Android phone) - for about a day. It suddenly dropped the internet connection early this afternoon, Sun, 11-Mar-2012, ~1220hrs PDT. I heard it go out because I was streaming NPR at the time.Using the B router, my desktop computer (connected via a wire) can still talk to my laptop (wireless), but neither of them can see the internet.When I swap back to the A router (wires only), it now has no internet connection either! But the desktop and the laptop (both wired) can still see each other via the (wired) router.When I remove the router from the network and connect the DSL modem directly to my desktop computer, I have internet access; it works fine! But not if a router is in the circuit.

(1) Router B seems to work because my wired desktop and my wireless laptop can communicate locally.

(2) Router A still works because my desktop and laptop can communicate with each other using a wired network hosted by the A router.

(3) The DSL modem seems to work because my desktop has internet access when connected directly to the modem.

(4) Neither of the routers can communicate with the internet through the DSL modem.

I spent an hour in a chat with Verizon tech support. I've power-cycled everything. I've reset both routers to default specs and reconfigured them. I've reset the DSL modem via its button. I've used different cables. It appears that neither of the routers can successfully communicate through the DSL modem to the internet. But they both used to. Why would it just suddenly stop connecting through the modem?

Scenarios:
computer <-> DSL modem <-> internet | works!
computer <-> either router <-> DSL modem <X> internet | NoGo
desktop <-> either router <-> laptop | ping OK

ipconfig /all results when connected directly to the DSL modem (internet connected):

Windows IP Configuration

Host Name . . . . . . . . . . . . : Serenity7
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No

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