onr thing to look at is how todays memory may not now be compatible with older 775 type boards
[for example]
Hi, I'm Jewel with Kingston Technical Support and would like to offer our assistance. It is possible that the HyperX 4GB memory modules are Single Rank as the latest builds of that part number are Single Rank. Up until recently 4GB modules were standard Dual Rank. Basically, the issue that can occur is that the memory module uses high capacity individual memory chips (DRAM) that the motherboard is not equipped to recognize. Usually, if a motherboard is able to recognized standard 8GB modules it should not have an issue recognizing Single Rank 4GB modules. A "1R" may be printed on the label which would indicate it as single rank. Otherwise, we can confirm this based on a reference number printed on the memory label that we can look up in our system. Other common issue with the DDR2/DDR3 combo motherboards that can be overlooked is that it only supports DDR2 OR DDR3 memory. This means you cannot have both DDR2 AND DDR3 memory installed at the same time, it is an either/or option. We do not currently support your PFG41C-M LX motherboard as we no longer manufacture memory that would be compatible with that motherboard. For any further assistance, please call us at 1-800-435-0640 (USA and Canada only) M - F 6am - 6pm PT and I or another available Technician will assist you. Please be sure to have the part in question on hand when you call.
theres a few brand that still offer compatible memory sticks but you have to look hard and may not be what you really want [it maybe down to take what you can get ]