This is a little project I'm doing at home.
I wanted to wire two rooms together (basically, the router is one room, and the switch is in the second room).
So I ran a CAT5 between the two rooms, and wired an RJ45 jack in each room.
I then hooked up the two jacks with two CAT5 cable to run it through the cable tester, and all 8 wires seem good.
Now, when I connect the switch and the router, the connection is unstable -- I ping the router and it barely holds on for two pings before it disconnects, and stays in that unstable state.

Just to make sure the router and the switch are ok, I connected them with long wire between the two rooms and the connection is absolutely stable, and pings continuously.

What could be the cause for the unstable connection? Especially that it pings a few times, so there IS a connection. But why is it unstable? And how come the cable tester says it's ok, but it's unstable?