Please help me: Memory problem

[Murdok00g]

I just recently purchased two 512MB DDR PC3200 400MHZ memory sticks online. I had a Kingston 512MB DDR PC2700 memory stick. I took out the old stick and put the two new ones in. When I fired up my computer I got the series of eight or more beeps. I took out one stick and it seemed to work fine. I made the stupid mistake of changing the DDR frequency from 200MHZ to 400MHZ. When my computer restarted it gave me the series of beeps again. From there, I tried the one new stick, my old stick, then both new sticks again. Each time I tried I got the series of beeps again. My computer will not get to the BIOS screen. It cuts on but nothing displays on the monitor. Can anyone tell me what my possable options are for how to fix this problem? Thank you. I've double checked the motherboard manual and it states that it supports up to PC3200 and 3GB of RAM.