Hi and welcome to TSG.
A few quick things to check that may help someone here to help you.
Are you connecting the monitor to the video connectors on the video controller card and not to the video connectors on the motherboard?
Are you sure you purchased the correct RAM modules?
Did you purchase the computer fully assembled and tested, with only the RAM missing?
What is the status of the EZ-Debug lights on the motherboard upon power up?
A few quick things to check that may help someone here to help you.
Are you connecting the monitor to the video connectors on the video controller card and not to the video connectors on the motherboard?
Are you sure you purchased the correct RAM modules?
Did you purchase the computer fully assembled and tested, with only the RAM missing?
What is the status of the EZ-Debug lights on the motherboard upon power up?