Replacement for Xeon X5472 and problems with RAM

All kind time of day!The question is: was XEON X3210 socket 775 mother GIGABYTE GA-P35-S3G socket 775,Opera 8GB,all worked.Changed percents on Xeon X5472 socket 771 with firmware modified BIOS mom. It worked,but there was one BIG BUT:the Nurse stopped to see half of the Opera.Put back the old percent-sees everything as it should,and no firmware do not.The changes in msconfig to the bulb, the lines of memory remapping in the BIOS, no.Dancing with a tambourine-type wipe,change slots, etc, etc. do not help.C new PERC sees all 8 GB,but there are 4 available.Somebody faced with similar?If Yes advise that....