Hello. What specific error are you getting? Attempt bringing the system to minimum to POST with the following components: 
Hello! I am here in dell community because i am having a error with a PowerEdge 2850 server. When i boot it everything seems to work but closer inspection both the blue and amber led on the front is off. Any usb devices (like a keyboard) will not power on. Both of the power supplies seems to be working perfectly fine with the error led off and both of the green led's on the power supply on. The hard drives on the front turns on but then after 2 seconds the led for all hard drives shut off and then when you replug the hard drives in it will turn on for 2 seconds then turn off.  I have tried :  Reset all of the ram chips and the cpu's in the case Replugin all of the hard drives in the server Tried multiple of monitors tried just using wall power insted of a power brick or a surge protector and tried to only run off of one raid, Everything ends in the same result  I have no idea what else to do so im just going to ask the community of dell. Thanks!
PowerEdge 2850 Post Error, no display, usb devices are not working and all 
drives are off (kinda)