I too, had an issue with an Asus M3n78-Pro Motherboard. I built a new computer and shortly after I built it-within a couple of weeks, it started this 1 long beep with 2 short beeps business. I scoured the internet looking for a solution and EVERYWHERE I looked-everyone was saying that it indicates a Video Card Problem. After several months of NOT being able to use my new quad-core computer, I finally wrote directly to ASUS tech support. They replied back, indicating it was a MEMORY problem, NOT a video card issue. I followed their suggestion and removed ALL the memory. GUESS WHAT-the computer booted. Before that-I got NOTHING, just a blank, black screen. With NO moemory in the motherboard-I could access the BIOS.
After trying all 4 memory sticks, I wound up with 2 bad sticks. G-Skill brand that I bought from NewEgg. Fortunately, I was able to exchange the defective sticks. The computer worked fine with the 2 sticks, but worked even BETTER after I got the replacement sticks of 2 2GB chips. Now, it's flying with 8 GB of memory. Another issue I had with beeps was for the last 2 years, I was getting 3 very short, fast beeps. The other night, my power supply finally went out. Computer would start and stay on for only a few minutes, then just shut off. After replacing the power supply, it no longer gave me the 3 short, fast beeps.
These were DIFFERENT though, than the 1 long, 2 short beeps. They were all 3 very short, fast beep, beep, beep.
1 long...2 short......BAD MEMORY CHIPS
3 short, fast...........BAD POWER SUPPLY