Dimension 8400 desktop motherboard

Dell uses a proprietary motherboard (physical size of the motherboard) and a proprietary and undocumented front panel connector.  The only thing that will fit in there is another 8400 motherboard.   If the motherboard is bad (and you also want another CPU), you need to weigh the costs compared to buying a new PC - a new motherboard and CPU will put well along to a new PC.  Dell, if they have a replacement motherboard from reports can be relatively expensive.  There are 3rd party dealers that sell refurbished Dell motherboards (do a google search for an 8400 motherboard).  I can't vouch for the 3rd party boards but I know several have bought them for other models. 

You could also opt for a Retail motherboard that will use that CPU (may be hard to find) and then also buy a new case and reuse the hard drive, optical drives, etc from the Dell.  If you go with a non Dell motherboard you will also need a new copy of Windows, as the Dell's will only install on a system with a Dell BIOS.  Again, you are looking at spending $$ near to a new PC. 

I've given you some options, but to be blunt a new PC is the best option.

I have  8400 that just has trouble.  The red light from the motherboard is showing red constantly but moments after turning the tower on button the processor fan starts going faster and will not return to normal speed, but goes at high speed. There is no display on the monitor. Support thinks it may be the motherboard.  and the part number for the board is M8970.  I removed the microprocessor from the board and turned it on again, but it went high speed again.. Does anyone know where to buy a mother board and processor. the processor is C3827, 80547, 4 Prescott DT, 3.4 GHZ, 1 MEGB 800FSB, socket-T.  Any suggestions?

Dr. Hall

You can buy a Dell OEM 8400 motherboard from HERE

The exsisting socket LGA-775 processor can be reinstalled in the new motherboard.

Bev.

[quote user="Dr. Hall"] I have  8400 that just has trouble.  The red light from the motherboard is showing red constantly but moments after turning the tower on button the processor fan starts going faster and will not return to normal speed, but goes at high speed. There is no display on the monitor. Support thinks it may be the motherboard.  and the part number for the board is M8970.  I removed the microprocessor from the board and turned it on again, but it went high speed again.. Does anyone know where to buy a mother board and processor. the processor is C3827, 80547, 4 Prescott DT, 3.4 GHZ, 1 MEGB 800FSB, socket-T.  Any suggestions?

Dr. Hall

You can buy a Dell OEM 8400 motherboard from HERE

The exsisting socket LGA-775 processor can be reinstalled in the new motherboard.

Bev.

I took your suggestion and got a motherboard from HERE as nobody else had one and the price was fairly good.  I installed the motherboard and found that it required a re-installing of Windows XP sp2 to get it to boot up, I reinatalled all the software Cds.  It is now up and running good.  Thanks BEV   This community seems to be pretty good.  Also some experienced computer people have stated that their personal view is that presently Dell has the best reputation at this time.  Remember things will be some what slower as layoffs have occured in a number of companies.  I have a XPS Studio computer I will get yet into the future.

Dr. Hall

Please to hear that the 8400 is running again and I'm happy to have helped.

Bev.