Your motherboard manual should have a list of it's "beep codes". Look up what problem your particular pattern represents.
While this may narrow the problem down a little bit, the best thing to do (if you already haven't) is to strip your new system down to it's bare essentials: motherboard, processor (with HSF!), ram, HD, floppy and video card. Make sure all devices and cables are well seated. See if will boot then. Then add components one at a time. Very often you can build up the entire system this way without any of the conflicts that arose trying to boot up as a complete unit -- don't ask me why.
Good luck.