Pc don't work

Question

Hi! I have a problem with my motherboard Asus P5PL2 .
I hwe already a memory Zeppelin 512Mb DDR2 533Mhz and i buy another one Memorie Kingmax FBGA Mars 512MB DDR2 533MHz PC4300 and now the PC stop to the memory test. If i tahe out the new memory the PC start.
What is the problem and how i can resolve it?
Thank you i will wait for an answer