If you have the same issue on 2 different motherboard, most likely it is a defective processor.
Make sure that both motherboards are fully compatible with that processor, keep in mind that the fact that the motherboards are based on socket 775, it does not make the motherboard compatible with the processor, that is the reason that all motherboard manufacturers have a list of supported processors for each of their motherboards.
If this is a 2nd hand processor, I would recommend contacting the first owner for any exchange option.
To determine if the processor is being properly recognized by the system you can run the Intel® Processor Identification Utility.
You can download the Intel® Processor Identification Utility at: