|Just to clarify...|
This is a home built PC, a desktop or similar; it boots - bu does "anything show on the display?
If no display at any time, how do you know the RAM etc. are ok?
Does the monitor power up - and remain in active mode; i.e. doesn't go into or indicate it's in standby mode?
Check cable to display - is it securely installed both ends; and is the graphic card scurely installed its slot? Presumesof course power into monitor is Ok...
Are there any "beeps"?
Did the system work previously?