|Looking again at your diagram the only thing that pops into my mind is to try connecting the Belkin to the MSI from LAN port to LAN port. Going from LAN port on the Belkin to WAN port on the MSI just adds one more layer of complexity and therefore, one more thing that can go wrong.|
Click on my name in any of my responses and read my "how-to" guide on adding a second router. Essentially, this is what you've done. Look at the "LAN port to LAN port" connection scenario.
It may also be that your Linksys router is in need of replacing. Before you replace it though, try two things after ensuring all IP addressing is correct.
1) Recycle the power on the Linksys (ie: unplug it, count to 10, plug it back in
2) Reset the Linksys to factory defaults (ie: hold reset button in for 10 seconds) and reconfigure it.
If either of the above two troubleshooting steps work, then you should be ok. Sometimes these SOHO Routers just seem to lose their marbles and recycling the power can fix the problem.
If neither works, I'd highly recommend replacing the unit. If it comes to that, look at a Linksys WRT54GL. We're using those here at work for insecure in-house wireless access to the internet for visitors. Tomato runs on them beautifully and I find they're actually pretty robust considering they're not enterprise level equipment.