I just successfully upgraded to a X5670 6 core CPU but now DIMM slot 1 has red led and not recognized. Dimm slot 2 is fine. I swapped the 16GB 1333 DIMMs between slots and still slot 1 not recognized so doesn't seem to be a problem with the DIMMs. However, If I put the DIMMS in slots 2 & 3, no problem. What could be the issue with slot 1?