As you add RAM, two things happen. The memory system slows a little and the power supply needs are higher. Unless you have a power supply of at least 100 watts more than you think you need, the issue is typical. If the power is sufficient, and it fails the initial POST, then you call the motherboard supplier and have them swap it out.
I am running win-xp-he os.My motherboard is a GigaByte GA-7VT600-L with the latest upgrade BIOS (Award). The MB supports 3gb DDR PC 2700 memory. I had been running with two 512mb DDR sticks. I added an additional stick of 256mb DDR in the third memory socket. All works well except when I reboot; I get a series of long beeps. I can hit my reset button and the PC boots to windows normally. When I restart the PC after complete shutdown, everything works normally. What is my problem?