In a flurry of blurry-eyed activity, I plugged in the MagJack of one of my Ethernet dongles into a powered up Pixelnet 4 Port Passive Hub. Now neither of the lights on the MagJack light-up anymore when I plug in an ethernet cable from my computer. Nor is there an output signal coming out the RJ45 jack on the other side. The green LED is lit and I was able to successfully reprogram and read the PIC. Since I has some extra ones lying around, I replaced the optocouplers and ST485BN chips but no difference.
Any suggestions as to what to try next would be much appreciated.