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I have a packard bell Imedia 4145 about 18 months old.

It shuts down soon after I switch it on. It will get as far as starting to load windows then shut off. Each time I turn it on it runs for a shorter period - after 2 or 3 attempts it won't even load the bios.

If I leave it overnight and then switch it on, it will load the bios and start to load windows again.

I suspect the problem is a temperature sensor somewhere giving a false reading - it never stays on for more than a minute. In that time I doubt that it would really get hot enough to

It gives a POST beep ok, and I have tried the following cleaning out the case and mobo switching memory cards around and running with just one disconnecting HDD and DVD drive disconnecting video card checked the fans and heatsink bonding to processor - all seem ok. put the HDD in an external case and checked it on another computer - seems to be fine

Next steps I am contemplating getting another power supply unit - maybe the one I have is malfunctioning getting another mobo - don't think I would be able to replace a defective temp sensor Any suggestions ? - thanks in advance

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Your thinking is certainly along the right lines. I would certainly be inclined to try a replacement PSU. If you can borrow one off a friend to just test with then so much the better.

I would also try running the motherboard outside the case with as little hardware attached to it as possible to rule out anything shorting with the case.

Pay special attention to the CPU and heatsink. It could be that the thermal bond between the two has broken down and needs replacing. A Remove the heatsink, clean off the old thermal compound with a little rubbing alcohol, and replace the heatsink using a new layer of thermal compound.

If all else fails, and you're sure the CPU is not actually overheating, there may be a setting in the BIOS to disable the thermal sensor - but if there is a problem with heat build-up in the CPU then you could fry your CPU doing this.

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Thanks MattActually I reset the BIOS to factory settings but that didn't help. I also took out the BIOS battery for a few hours to help ensure it went back to default settings – Gerry Neville Apr 23 '11 at 10:06
Thanks Matt I did reset the bios to default settings but that didn't help. I doubt that the computer really is overheating, since I think it is unlikely it would get too hot within a minute of starting up ? – Gerry Neville Apr 23 '11 at 10:13
If the heat sink is failing it can take a matter of seconds for the CPU to overheat. – Majenko Apr 23 '11 at 10:25
@Gerry Nevilly, it's actually entirely possible for a poorly ventilated/cooled computer to crash on startup :) mine did it before I got it fixed. – n0pe Apr 26 '11 at 10:44

Try booting into a linux LiveCD just to rule out anything weird with drivers and such. When using the LiveCD, open a terminal and type sensors you'll able to see all the temperatures inside your computer.

Note that this can also be checked in the BIOS (for most chips).

I would check all your options before having to buy a new PSU or mobo.

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