I think remodelers manhandled the Cat5e cable one too many times that runs under the house to bridge my family room and office, as it's no longer working :(
I would try putting a new RJ45 connector on the roughed-up end, but I can't find my damned crimp tool. I could've sworn it was with my soldering kit, but clearly they got separated at some point. Argh.
For now I'm bridging the office and family room routers over 5GHz WiFi via Tomato's Media Bridge mode. This is not ideal because WiFi has both a higher base latency and occasional burps that are even worse.
Update: After much hand-wringing, I decided to buy a $9 keystone jack instead of a new crimper. Came with a cheap plastic punch tool, but was much less fiddly than jamming the wires into an RJ-45 connector for crimping.
...And, crucially, it works! I'm sending this via the Cat5e cable in question, at 1gbps.