Randomly shutting down and restarting - blinking LED2

This computer is EMC 2008. I replaced the power supply several years ago and the computer has not been used that much since that replacement.

When I power up the computer it randomly shuts down and restarts itself. I opened the unit to observe what is going inside while this happens.

All of the below has been happening while the computer back is open, so there is plenty of air.

The right fan is blowing out hot air.

The left fan is drawing in air.

At start-up all 3 internal LEDs come on normally. Then the computer will shut itself down...then start back up.

I've timed the intervals between the startups and shutdowns and it's seems to be 2min:30sec (+ or -) between shut downs and startups.

When the computer shuts itself down internal LED 2 blinks in unison with the white light that on the FRONT right of the machine.

If left alone the computer will go through this sequence endlessly... starting up... shutting down... starting up ... shutting down...

Here is what I have done:

compressed air in the left fan and right fan.

removed right fan duct to check for clogging and debris - nothing in there

reset pram

replaced pram battery

reset smu

reseated RAM - and switched locations

Could it be the power supply again? The computer doesn't stay on long enough for me to install a CPU temperature checker.

Thanks in advance for the advice...


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1 Answer

Chosen Solution

1. A Flashing power LED once per second - bad RAM, no RAM

2. Three flashes, a pause, and three more flashes (occurs continuously) - marginal RAM Maybe you bumped the RAM reseat and check.

3. Could be failing logic board again... LED #1 indicates power problem (yours is steady=OK), #2 is CPU problem... which could be the processor or the logic board.

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Hi -

LED #1 is the power LED... right? What does it mean when LED #2 is blinking once per second in concert with the light on the front right?

I found an article last night about the thermal paste on the heatsink. I took the cover off the heatsink last night and blew out some stuff, but it looks like I would have to pull out the entire logic board to get to the thermal paste.

I managed to load a temperature monitor on last night after clearing out the heatsink. The CPU temp and drive temp were both in the 150-160 degree range, while the back cover is still off.

Is it possible the computer is going into thermal sleep when the processor gets too hot?


If you open the heat sink you must apply new paste, and all the old paste must be cleared off. Re: LED #2 -Follow these steps. Yes if heat sensors trip, and fans don't cool the machine, it sort of goes into cardiac arrest (freezing) to allow the CPU to cool manually.


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