A) The first thing to check is the Power Supply.Cannot depend on LED's lighting, or fans spinning; to include the Power Supply fan.A Power Supply with a weak voltage power rail, will have enough power to light those simpy LED's, and maybe spin fans; but NOT enough power to turn the Processor (CPU) on.1) If ALL of those LED's (Light Emitting Diode), were on at once; they would use less than 1 Watt of power.2) EACH fan uses about 2 to 3 Watts.3) A typical CPU (Processor) can use 51 to 130 Watts. Just depends on what Processor it is.http://www.amazon.com/Intel-D865GBF-Socket-478-Motherboard/dp/B00009EQ08(Not trying to slam your motherboard Chris, but $219 bucks?You couldn't GIVE me that motherboard..........jus sayin')Uses the Intel 865G motherboard chipset,http://en.wikipedia.org/wiki/List_of_Intel_chipsets#Pentium_4_chipsetsScroll down a littleCan use Processors that need Up To 115 Watts. (Maybe higher)Did you test the 3 Main voltage power rails?3.3 Volts (DC), 5 Volts (DC), and 12 Volts (DC)What were the voltages?Or did you use a KNOWN to be good, Compatible power supply?How do you know it's good?Moving on..........B) I suppose an inspection of the Electrolytic Capacitors, should really be first. It is a visual inspection,http://capacitorlab.com/visible-failures/index.htmhttp://www.youtube.com/watch?v=Lut7MX5Dd_AHowever, you have replaced the motherboard. So we in good faith, have to assume the motherboard is good........(Or do we?)This would lead to the Thermal Paste, on top of the CPU (Processor), has dried out.Top of CPU, and bottom of finned Heatsink needs to be THOROUGHLY cleaned, and fresh, new Thermal Paste applied.C) No? Power Supply has been deemed to be good?Processor and bottom of Heatsink cleaned, fresh new Thermal Paste applied?(4-pin ATX +12 Volt wire plugged into motherboard?Power for the Processor,http://www.playtool.com/pages/psuconnectors/connectors.html#atx12v4 )......The motherboard is mounted to a Support Plate.The Support Plate can be a separate sheet of metal, or an integral part of the motherboard.Mounting the motherboard to the Support Plate, is accomplished with either plastic Spacers, or metal Standoff's.IF, a Standoff is NOT mounted to a motherboard mounting hole, and is just standing out there; there is a good chance it will touch one of the exposed solder joints, on the bottom of the motherboard; and short the motherboard out.Removing the 'offending' Standoff, or moving to an open motherboard mounting hole; may result in the motherboard working again.Along with the Standoff's are Fiber Washers.Rule of thumb is;Motherboard mounting hole has metal ring around it? No fiber washers are used.Motherboard mounting hole does NOT have a metal ring around it?Fiber washer is used on both sides of motherboard mounting hole.Let's consult the Intel D865BGF Product Guide,http://www.intel.com/support/motherboards/desktop/d865gbf/sb/cs-008983.htm?wapkw=d865gbfDoesn't say. Statement is, "Refer to your chassis manual for instructions on installing and removing the desktop board."Motherboard may get it's ground, from those metal ringed motherboard mounting holes. IF PRESENT.D) Motherboard is bad.Electrolytic Capacitors are bad. If they do not show outward signs of failure, the Electrolytic Paste inside could be dried up. Would show no outward signs of failure.Computer design engineers know this. They know the Electrolytic Paste inside is a chemical, and has a chemical reaction.The chemical breaks down over time.This is why computer design engineers use Electrolytic Capacitors, that are rated at TWICE of what is needed.When the capacitor breaks down to 50 percent good, it is still 100 percent good for the application.Now...................New/Old Stock, or not; that mobo is OLD.(MOtherBOard)E) Processor (CPU)Very rarely one goes out. Overclocking, and getting it too hot?Oh yeah. Bye-bye CPU.There is one other way, though.........A CPU (Processor) is the MOST, susceptible hardware component to Static shock.If whoever has been handling it has not followed Anti-Static Procedures, drill a hole through it, and put a chain through the hole.See? You've got a snazzy(?) necklace......Motherboard can be used for a Frisbee, too.F) Are you running a graphics card?Power Supply has enough power for it, and the rest of the computer system?Motherboard, Ram Memory, Case fans, CPU fan, optical drives (CD/DVD drive), and Harddrive/s.http://extreme.outervision.com/psucalculatorlite.jspG) IF, the graphics card requires a power cable, does your Power Supply have the necessary power cable?Post back in a Comment.Regards,joecoolvette
