I've had, in the past with older machines, graphics cards which had their own "startup screen" that showed before the system started to do POST. However, that doesn't sound like the case. So it takes 20 seconds before the system starts going through its POST? It could be an issue with your BIOS. Have you checked with the manufacturer to see if a new BIOS update is available? I might suggest contacting Asus for support on the board, perhaps it's a known issue with them. None of your hardware stands out as particularly "problematic". If you want the cleanest boot possible, did you remove the optical and hard drives to see how it POSTs with only cpu, mb, ram, and video?
After that, if that doesn't change it, remove the video card as well (leave the HDD and Optical out) and see if it beeps sooner. If so, video card may be it, but still check if it's not the PCI-Express bus on your board?
Edited by Nicholas Basso, 26 October 2011 - 05:02 PM.