Recently, I added two new computers to a LAN already running with two. This sounds simple, but due to wiring issues and the fact that I wanted the new PCs in a different area (and we had an extra router), I ended up making a network more complex than I can really troubleshoot myself. (I wish I could generalize the question, but since I can't isolate what exactly is causing the problem, the question can only really be answered after I give detailed information about it) So I have an SMC router, with 8 ports. This router has my modem connected into the WAN port, and two other cables connected, one to a PC, the other to my second router. This has always been the case, and I haven't had problems. The cord from my SMC's port is plugged into one of the standard ports on a Linksys wireless router (WRT54G) (not the WAN port, since it's acting as a Router and not a Gateway). Before, I had only one other port occupied on the Linksys router, running to my PC. Recently, I added two more computers practically adjacent to mine, filled up the non-WAN ports on the Linksys, and let it run. After some short time (I've never been able to time it, probably ~1 hour or so), the internet connection begins to slow to a crawl, and eventually stops entirely until I reset the SMC router.
What might be causing this?
The few networking classes I've taken make me think there's some kind of loop in the network, just because it's something that seems to gradually occur over time, but I wouldn't know how to find out whether or not that's the issue, and how to fix it. Are there possibly some routing options on both that I need to fiddle with to reduce the fail?
One important detail: Issues with the DHCP server had me turn it off for LAN for both routers, and I'm using static IP's of 192.168.2.(3-6), with the DNS server set as the IP for the router (192.168.2.1). I'm only bothering to mention this because it seems like it could be an issue with DNS servers rather than internet connectivity as a whole. Any advice on troubleshooting this?