Well, a cathode light is used for backlighting, or hardware mods. If you ever see a glowing PC fan that is not made up of LED's, then the bulb that is used is more than likely a cathode light. They use some kind of gas to create the light, so they are popular because manufacturers can shape the bulb to designs and whatnot.
Anyways, if you HDD is not locked, then that could be a problem. I think one of the wires on your chip has either mis-aligned (if it is solderless.) or has broken off. Although, it has been a while since I worked with HDD's, so I don't remember if you get an error if you boot with the retail bios on an unlocked HDD or not.
I would make sure your chip is on correctly, then I would lock the HDD if that fixes the problem.
Try switching to the retail drive first though. If it works (and backups boot), then it was either a faulty connection or your upgrade has died
