What you are hearing are warnings from the ASUS POST Reporter. ASUS uses the POST Reporter in many of its motherboards to alert the user to problems with the CPU, Memory, Video card, etc. Don't tear apart your system. ASUS made it easy for you by telling you EXACTLY what is wrong. Next time you boot the computer, record the exact sequence of the beeps.
Here is what you can determine from the beeps:
Long beeps in an endless loop means NO DRAM INSTALLED OR DETECTED. High frequency beeps when system is running means CPU OVERHEATED; CPU RUNNING AT A LOWER FREQUENCY. If it were the video card you would hear one long beep followed by three short beeps.
It sounds to me like your MB is telling you that it doesn't see your memory. The best thing to do is RE-SEAT the memory but bear in mind that without a Static Wrist Strap ($6.00 at most computer stores) you can damage or destroy your memory modules via the static electricity that your body conducts. Also, make sure that the tower's power cord is UNPLUGGED. Attach the clip end of your static strap to the computer's chassis before touching any of its internal components. When you re-seat your RAM, make sure that you push down on one end of the module at a time. Once both ends snap in, place firm pressure accross the length of the module to make sure that it is fully seated. Assuming that you have multiple memory modules, you may want to try installing a single module and re-booting before installing additional modules.
Good luck!