NB issue - power cuts out unexpectedly

After months of perfect behavior out of the saber since I rebuilt it, it started acting funny this weekend where it would shut off and I'd have to put the kill plug in in order to "reboot" it. It happens at random where I activate it and it loses power and stays dead until the kill plug cycles it. The first time it happened I figured the battery was probably exhausted, and I think it was close. It charged for somewhere around 7-10 hours before the light turned green on my charger, but it still happens. It is hit or miss when it would or wouldn't shut off. For example, last night I turned it on and it died four times in a row within 3-10 seconds of activation, then it stayed on and I left it running for 10 minutes, no problem. Based on my tests I could not find a correlation between the power loss and the FoC effect/physical impact on the saber.

I also noticed that one of the three main LEDs is out. (GGW tri-rebel, one G is out, FoC works fine) I haven't torn it apart yet to check the wiring, but I thought I should check here first before I do.

I don't know if this would factor in, but in addition to the GGW running off the NB I also have an accent LED tied into it to pick up the pulse effect as a crystal chamber using extremely fine wires, otherwise it's a textbook NB setup with a lithium ion 3.7V 3400 mAh. The accent LED is a standard low-power LED. Sound and FoC are fine...the power just cuts out seemingly at random to everything, including to the AV switch LED. We did put it through some pretty fierce dueling on Friday night, so I'm not sure if that would factor into it. And I know on Thursday all three LEDs were working.

Any ideas where I should start to troubleshoot?

Start with the solder connections on the Tri-Rebel. It's possible one of the connections to the inoperative G LED is loose, and is bouncing around and shorting things out.

Nailed it. Thanks SS. Really hard soldering on a heat sink :P

Ask me why I keep spare thermal tape pads around. :)

It's often easier to remove the star, resolder any bad connections, and reattach it, than it is to solder while it's still attached to the heatsink.

I have some arctic silver at my parents' house that I could try to replace the tape with, but this will hold for now. Has anyone tested thermal tape vs arctic silver?

Well, there's Arctic Silver Thermal Compound, and there's Arctic Silver Thermal Adhesive. For attaching the LED star to your heatsink, you'd want the adhesive. It's a two-part permanent adhesive.

The thermal compound will give great thermal transfer, but will not hold the LED star onto your heatsink.