Dell 8400 steady amber light, no diagnostic LEDs, high turbo fan

1) Switch the system on. Can you tell me if the power button is flashing amber or a solid amber? Please also tell me if you notice any diagnostics LEDs staying lit - these are labelled 1,2,3 and 4 and are near the front headphone sockets
2) Please remove all peripherals at the back of the system and switch the system on. Does this affect the power button LED or diagnostic LEDs
3) Have you added any components to the system e.g. video cards, sound cards etc...
4) Please open the system and remove the following components:
a) Power and data cables from hard drives and optical drivesb) Any PCI/PCI-Express expansion cardsc) All memory from the systemd) The system fan
5) With the above removed, please reconnect the power cord to the back of the system and switch the system on. Please make a note of what happens with the power button LED and the diagnostic LEDs
6) If there are no changes to the power button LED or diagnostic LEDs, please remove the power cord from the back of the system and remove the following components:
a) I/O panel cableb) CMOS battery
7) With the I/O panel cable and CMOS battery removed, please connect the power cord to the back of the system. The system should automatically try to switch on. Do you hear any beeps from the system? If so, can you tell us exactly what you hear?
If you need any assistance with removing these components, please see the User Manual here: http://support.euro.dell.com/support/edocs/systems/op380/en/index.htm
Please keep us updated on how you get on!

Can you tell if your hard drive is running? You can here it or feel it spinning. Are the fans running? If no, I'm 99% sure you need to replace your power supply and/or motherboard. This kind of thing usually happens after a power surge.

Your power supply or motherboard has a problem. You can try getting a power supply on the internet ( $25 to $75) first. If no go then motherboard (about $100 to $200 ). The 8400 is about 6 years old which is the average lifespan of computers. One last thing you can try is removing the heatsink assembly and re-seating the processor. You have to clean the old thermal compound from the CPU chip and heat sink and reapply the compound (thermal paste). You might be better off buying a new computer from Walmart.

May be serious. See if the power light goes amber after power up. I had (have - still siting in my basement) one that did same. Power up, fans sound like 747 taking off. Power light goes and stays amber. This is USUALLY caused by bad capacitors on the mother board. Known GX280 problem going back. If you look on the motherboard, the capacitors should have flat tops and not leaking. If the are rounded or leaking, the MB has probably gone bad.

I obviously can not be 100% sure about this as the unit is not here.

You can google "gx280 solid amber light loud fan" and see the issues. Here is one such link.

http://en.community.dell.com/support-forums/desktop/f/3514/p/19253544/19414291.aspx

The POWER and DIAG LEDs can give you information. If no DIAG LED look at the POWER LED
http://www.fixya.com/support/r4282412-find_no_post_diagnostic_information_dell
Flashing amber, most likely the power supply
Solid Amber, motherboard or item plugged into the motherboard (Expansion card, external connection etc.)

Steady amber power LED is indicative of a problem with the motherboard. Remove all external connections except power, remove all PCI Cards, ram, disconnect power from all drives, turn on see if power LED is still steady amber. If it is, more than likely the motherboard has a failure. Also check to see if the CPU heatsink is firmly seated (The plastic retainer has been known to fail causing the CPU to overheat)

As a hardware repair technician at a local university, I have seen the amber power light problem on quite a few Dell computers. If the machine is in warranty, Dell insists the power supply be the first thing replaced, even if it tests ok. If that does not do it, then they send me a new motherboard. Of the dozens of machines that have had this problem, only 1 of them needed a new motherboard. The power supply alone resolved the problem on all the rest. I have found this to be true on out-of-warranty systems as well.

Which fan?, the cpu fan or the cpu fan?

Most Dell pc come with a below average power supply. I recommend replacing your power supply with a better one. Do a search on Google for a good replacement power supply for you Dell 8400.

Please rate response.

I have a small business where I have worked on PCs for the past 14 years. I have had some of my clients that have brought me a few of these Dell 8400 to work on with the same problem. Will not boot and loop the start up, along with sounding like a leaf blower. After much trial and error i.e. Heat sink,cooling fan, power supply and motherboards. The first one I worked with by changing the heat sink, worked for about a week, then started doing the same thing. Replaced the Power supply with no results, same issue. Next was the Motherboard, still same issue. Last I pulled the processor out and found that the processor had over-heated and was damaged. In all I had well over $500.00 dollars invested and countless hours. Still the machine did not work, and still needed more work. Since this time I have had a few more of these machines cross my path. My suggestion is to scrap it and purchase a new PC. This is not one of Dell's better designs, and there is a tech issue from Dell related to this problem with the heatsink and the machine itself in the tech support on the Dell site. It states that they had a bad batch of heatsinks, but only replaced them under warranty.
Salvage what you can and build or have someone build you a clone.

If the power light is steady amber, a device might be malfunctioning or incorrectly installed.

• Remove and then reinstall the memory modules.
  
  
• Remove and then reinstall any cards.
  
  
• Remove and then reinstall the graphics card, if applicable.
  

Disconect fan , see if it starts.