r61e - adding ram

I tried to add ram - 2x2GB instead of 1 GB (Kingston 2GB DDR2 SO DIMM
667 CL5). Each of them works fine, when installed separately, but they
don't work installed together - Vista does not start.

Model: r61e 7649-w1z
System: Vista Business Basic

Thanks in advance for a hint
cisiek@[]>