What happens when all four red LEDs stay on and no video on boards such as P4DC6+II, X5DP6, X5DPR...?
If all four LEDs are on meaning that either system cannot recognize CPU, the CPU is bad or there isn't enough power supplied into the CPU. Please check the following: (a) Make sure CPUs are properly seated (b) Make sure CPU is good (c) Make sure 8-pin 12V power connector is properly connected.