T400 Display/Lights Not Working

I have a Lenovo T400, and today my display stopped working completely.

I was in class, I had one browser open, and I closed my laptop in order to take notes in my binder. Everything was working fine. When I opened it back up again, the display would not turn on. The only light that was flashing was the WiFi symbol. I tried to put it to sleep, turn it back on, nothing was working.

At this point, I turned the laptop off manually. Now none of the lights go on, and this is including battery status. When I plug the power into my ThinkPad, the power symbols don't even light up. However, I can still hear the computer turn on, and the only light that is on is the CD Drive. Again, my computer was completely fine before I closed the cover for about 10 minutes.

Any thoughts on how to troubleshoot this?

 

I just connected my T400 to an external display, and powered it up. A program called "Startup Repair" ran, indicating that my computer failed to start. It said it did some repairs, I restarted my computer, and now it is running.

However, this time the only light that appears to be on is once again the WiFi symbol. It is plugged in, and the power symbols still do not light up. When I disconnected the external display, nothing shows up on the laptop display.

Edit: Also, my base warranty expired about a week ago...

 

With symptoms like that I would strongly suspect the LCD cable. It might either be damaged or loose, especially since it powers everything in your lid, including the display inverter(where your indicator lights are; if you have an LED T400 it's an LED board instead of an inverter). The best-case scenario is that it's lose at the motherboard connection and will only take unplugging and replugging it to get it to work fine. Worst case is replacing the LCD cable. If you haven't worked on a notebook before it's a bit daunting, but it can be done. The cable itself isn't that expensive, thankfully.