Here are the memory specs for this computer:
Memory module capacities - 256 MB, 512 MB, and 1 GB
Memory type - 400 MHz or 533 MHz 1.8-V DDR2 SDRAM SODIMM
Minimum memory - 256 MB
Maximum memory - 2 GB
The 667 MHz is beyond the 533 MHz specified. Sometimes, boards can handle this, and sometimes not. This may be your problem. Try installing the correct memory per Dell's specs.
For more info, see: http://support.dell.com/support/edocs/systems/latd610/en/index.htm