Computer Shuts off upon start-up

[Country_Girl]

Okay, prior to the problem of the thread title, for about 3 weeks everytime I would start my PC the CPU Fan would kick on "overdrive/high intensity" fairly often...I know that when the system gets hot this is normal, but it was doing it more & more frequently.

Finally, 2 days in a row- after only having the system running for maybe 30 minutes it just shut itself off & restarted on its own.

I opened it up & cleaned off all the fans...disconnected the CPU Fan from the heatsink to make sure I got all the dust out of there.

Then comes the new problem...after I did that, upon start up the CPU Fan is immediately on "high" (doesn't even out to a lower setting, always on high intensity).  And as soon as it starts to boot, now it immediately shuts down- will try to restart, and shut down again.

I took the PC to Best Buy for a diagnostic.  Replacing the Power Supply did not resolve the issue.  They said it's either the motherboard or the processor.  They said there was no way to test for which it was- would have to start with the motherboard & if that wasn't it, then the processor was the problem.  Said estimated repair would be equal to that of a new PC & did not reccomment fixing it.  I've been told by several friends that I need a second opinion, that Best Buy is just trying to get me to purchase a new PC.  And I really don't want to purchase a new one, this one is only 1.5 yrs old.

I noticed when I had disconnected the CPU Fan from the heatsink, I got some metallic goo on my hands.  This I am guessing is Thermal Compound.  Is it possible that rubbing some of this off is my start-up problem?  Maybe a new coating will resolve this issue?

Or if anyone has any other ideas on possible problems?

[Aegis]

Yes -- I am not the most expert here, but I would recommend a new coat of the thermal paste.  It is possible there is some damage, but it seems the computer is protecting itself by shutting down, which (although frustrating) is probably a good sign.

(The paste fills in microscopic gaps in the surface of the central processing unit, and helps more efficiently transfer heat from the processor to the heat sink and fan.)

[homer]

in addition to what aegis was saying about placing a new coat of thermal compound on your CPU, just remember to remove the old thermal compound. i use isopropyl rubbing alcohol @ 70% with coffee filters (or any other lint-free rag), and it works very well to remove the old paste. also, one of the most common causes of the CPU overheating is incorrectly mounted heatsinks!!! make 100% sure the heatsink is mounted properly! if this is an intel CPU motherboard, make sure that all the clips are locked in place.

[Country_Girl]

Thanks very much for the replies, much appriciated 

homer- thanks for the suggestion reguarding cleaning off the old paste, that would have been my next question (what to use).  As far as what u said about incorrectly mounted heatsinks- I didn't build the PC, was store bought, is it still possible it's not mounted right?  If so, why is it giveing me a problem now- not when I bought the system?

[homer]

is it still possible it's not mounted right?

yes.

If so, why is it giving me a problem now- not when I bought the system?

assuming you have an intel CPU, stock intel CPU heatsinks use a type of pushbutton mechanism to lock it into place. it is very common for inexperienced people to firmly attach the heatsink to the motherboard, but forget to lock it into place. without locking the heatsink in place, the fan will eventually vibrate the heatsink loose. here is a good guide for installing a stock intel heatsink.

http://www.hardwarezone.com/articles/view.php?cid=19&id=1215&pg=6

[patio]

Did you hook up the CPU fan properly after dis-assembling ? ?
If it is on High all the time it may be the leads are backwards...consult your MBoard manual.
You may want to consider replacing it if the machine is more than 3-4 years old.

[Country_Girl]

Ok, new problem grrrr....

I have not attempted to start the machine up since I got it back from diagnostics.  After applying the thermal paste I gave it a go & yay! It started up, did not shut down.

New problem is the Monitor Shuts off & goes to sleep upon startup.  Tried turning it off & on, hitting keys, clicking mouse- but no luck.  Can't even get on the starup screen because of this.  All the connections are secure.

So I open the PC back up, noticed a set of wires weren't even plugged back in to a set of prongs.  Thought maybe that was it- but no luck.  I know there is nothing wrong with the video card because BB tested it.

Is there something else I should look for that might be lose & causeing this issue?

[brett74]

I had this problem with a computer where I worked and it basically froze up when in standby mode then when we restarted the pc it was fine I don't know if that's the problem but you said that the connections are secure right. What I would do right now is pull the vid card out just to double check and then put it back in. The reason the monitor went into sleep mode cause it's not getting the signal it needs to be awake.it could be as simple as pulling the vid card out and putting it back in.