Fan always running on Presario 2700 laptop followed by immediate shutdown

I have a Compaq Presario 2700 laptop.  Within 15 seconds of turning the machine on, the processor fan runs and after 5 more seconds, the main fan turns on.  Both are running at high speed.  After about 60 seconds (less time than the machine takes to boot completely), the machine shuts itself off instantly.  

My first thought was dust, but after cleaning it still powers off.  I checked some other threads that mention the heatsink becoming electrically diconnected from the motherboard and causing a ground fault, but I have used silver epoxy on the lockdown nuts and now the electrical conductivity is fine.  

I have checked the heatsink, and it doesn't seem warm (at least cooler than my other laptop that does work properly).  Since the fan runs from startup, I believe this is hardware, not Windows related.  Both fans are functional.  The BIOS does not have a temperature monitor from what I can tell and Compaq doesn't seem to offer a diagnostic CD from what I can find on the webstie and the media I have from purchasing it.  The machine is about 4 years old, way past warranty.  Any advice for things to try or diagnostics that can be run?  Since the machine can't be on very long, I am limited by the tests I can run.  Any diagnostic ideas would be greatly appreciated.  Thanks!
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couple of basic things to test... using only battery to boot, then take the battery completly out, using only plug to boot, see if theres any difference...
nma126Author Commented:
I have checked that, sorry for not mentioning.  The machine repsonds the same whether it is on battery or AC.
does it have added memory? take the added one out and test
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any added devices? usb/pcmcia/firewire, take all that off too
btw, what OS? have you tried going to safe mode? same results?
if you say the fans run at very high speed even from startup, maybe the mobo is bad, the sensor thinks its overheating and shutsdown...
maybe it needs some spring cleaning?

Depending on your model, vents can be found on the side, back, and/or bottom of your notebook PC. These vents allow air to flow through the PC and keep it cool. Buildup inside these vents impedes the cooling process. Purchase a can of compressed air (available at most computer retailers) and blow them out.
nma126Author Commented:
Thanks for the assistance, but I have checked for airflow and cleaned the vents with air, but to no avaiil.  To answer Baconyl, I haven't added any devices.  The machine is stripped to its minimum.  I have not swapped memory, don't have anything spare so that is an issue.  The OS is XP Home, but since this issue occurs even in the BIOS, the OS isn't important, nor is safe mode.  Any advice on this mobo and the heat sensor?  I don't know where it is or if I can replace it.  Any info?
Remove the thermal compound (whatever was used) between the processor and the heatsink.
Replace it with some properly applied thermal paste.

If your processor is getting too hot and the thermal paste is bad/shot then the heatsink would not be getting as warm as it should.
- The cool heatsink could BE the problem. The heat from the CPU isn't getting TO the heatsink.
>>  some other threads that mention the heatsink becoming electrically diconnected from the motherboard and causing a ground fault, but I have used silver epoxy on the lockdown nuts and now the electrical conductivity is fine.  <<       this seems totally wrong.
The heatsink does not need to be electrically connected, but thermally, to be able to transfer the heat from the CPU to the HS. The same thing applies to the lock down nuts, which only have the mechanical function of holding the cpu and heatsink tightened together. they do not require the heatpaste. Did you not short anything with it? It looks like you put on TOO MUCH ! only a tiny drop on the CPU is required.
The function of the thermal compound is just to fill up all air gaps between CPU and HS, to maximise the transfer of heat. i suggest using Artic silver for it :
for Diagnostics, i would try booting without disk, cd, or even ram.
nma126Author Commented:
I will look into getting a tighter connection between the processor and heatsink, but even with applying new thermal compound the problem continues.
In response to Nobus, this model Compaq notebook requires electrical connection between the mobo and heatsink as a safety interlock.  I have, of course, made sure there is thermal connection between the HS and CPU.  I have not used too much cmpd and I know I have not shorted anything, but I cannot rule out something else being shorting causing my problems.  Hence the question about diagnostics.
What do you mean by booting w/out disk, cd, or RAM?  Do mean just to the BIOS?  If so, what does this tell me?  There is no temp monitor there and the machine still shuts itself off in the BIOS.
remove the devices for booting, they can be bad
Do not over tighten your heatsink or processor mounting.
They are 'snug' not 'tight'.
Two fingers max on the screw (or nut) driver.
Too tight and you may cause a flex in a part (motherboard/heatsink) and the curve created will reduce contact (possibly even electrical in a socket) and reduce heat transfer.
Your electrical contact on the heatsink is actually to reduce EMI (static, electrical noise).
Same idea as grounded sheilding in wire.

Remove all removable parts.
Floppy, CD, hard drive, any mini-PCI cards (if you have them).
Try and boot. Tell us what happens. (Beep codes, lights, fans, noises)
Now remove the RAM.
Try and boot. Tell us what happens.
Now remove the CPU.
Try and boot. Tell us what happens.
Now put the RAM back.
Try and boot. Tell us what happens.

If -anywhere- along the way anything significant changes stop there and tell us before you continue.
nma126Author Commented:
Thanks for everyone's assistance, but it turns out the problem was the heatsink-MOBO connection.  After re-epoxying 2 more times, I finally got a good connnection.  Since then, all is working well.  I didn't want to go through previously mentioned methods of drillign a hole through the bottom of the case, so i hope this epoxy holds up.  Either way, bad design by Compaq.  Thanks again.
Yes I suggested that in my first post.. It's not called epoxy though.. It's thermal paste..
nma126Author Commented:
I beg to differ.  If you look at threads about this machine, there is a problem with this mobo design.  Trust me, I know the difference.  So much for Experts Exchange- looks you don't do your homework.  Thanks anyway.  
Then it's Thermal Adhesive, that minor does not change the validity of what I said.
The terms are widely used interchangeably in discussion.

As I posted...
""Remove the thermal compound (whatever was used) between the processor and the heatsink.""
""- The cool heatsink could BE the problem. The heat from the CPU isn't getting TO the heatsink.""

As you discovered, that was exactly the problem.
It is a typical heating problem if computer shuts down.your processor is overheating. Try to change the processor .If the problem is not solved then there must be  problem in the Core Supply of motherboard.
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