i`m going to take it that you did take the time to read all the way through the manual that came with the new motherboard you bought. I only say this because about 50 to 60% of the time the honest answer is no i have not.
If the case it`s self explanatory as why in most cases the user has not and why the board is not working right or powering up.
Due to a lack of power connectors from the PSU to all the power points of the motherboard that require power in order for it to work right and post, and positions on where you exactly need to place ram or memory modules into the slots provided for them on the motherboard in the right positions based on the amount of memory sticks used.
Because failing to check that results in the board also not powering up right and posting.
If you read the manual the red light means the board requires more power, meaning you didn`t read the manual in most cases.
It means that one of the extra atx power blocks is not connected from the psu to the motherboard, for example you may have only four of the pins connected other than the eight required.
Or missed them out.
If the board has multiple led lights for the Pci-e graphics card, CPU, Memory, any single light still lit indicates what section of the board you should be looking at, in your case since the red light is lit on the board for power.
You have a power problem, or a lack of power and why the led light is a fixed lit red. So power to the motherboard from the Psu needs to be double checked. And is the cause as to why the board is not posting right, or fully in most cases.
Most likely the extra atx 12v eight or four has not been plugged in to the motherboard from the psu.
Go have a check.