G4 Quicksilver Dual 1Ghz Shuts Down on it's own!

I'm not sure what's going on here but I have a G4 Quicksilver 1Ghz Dual w/ 1.5 Gb of Ram running OS X 10.4.11. On no predictable schedule, it decides to shut down without notice or shut down sequence . . . it's like the power gets shut off. Poof!

I've checked my surge-pro and it's working properly. My best guess is perhaps the machine has become sentient and is protecting itself from heat damage. The real question is why and are there ways I can increase the cooling ability of my heatsink/fan set up?

I may way off base with the diagnosis and if so I'd love to be clued in if anybody else has run into this and figured it out! Any help would be greatly appreciated! ;D

Heat would be the first suspect. How long since you took the Quicksilver apart, cleaned all the air inlets, outlets and fans? Also what graphics card are you running and have you checked the fan unit, if any on the card, is actually running? You can do a search of Apple Discussions re failed fan problems on graphics cards without mention a model.

I was inside it a couple weeks back when I installed a new hard drive and additional memory. I didn't notice any clogged fans or heat sinks. I'll give it another check for good measure. Any other things I should look into?

There is a heat sensor that is designed to do exactly what harryb2448 describes. It is either accurately dealing with a problem or it is screwy! Install iStat, it will give you an good reading of the mobo/processor temperatures.