Explain yourself better.
What memory added? Provide part numbers.
What storage added? Provide part numbers.
What peripherals (keyboards, mice, etc.) connected? Provide part numbers.
Using stock power supply? If not, provide part number for replacement.
Using stock chassis? If not, remove board from this chassis and test again.
What monitor(s) connected?
How are the monitor(s) connected (i.e. what cable(s), adapter(s), dongle(s), etc. used)? Provide part numbers or link.
Is this a new build or did it work previously?
If it worked previously, what changed?
What have you tried to do about the problem?
When you press the power button, does the power LED flash? If so, what is flash pattern?