This may be a driver issue. What are your complete system specs including Windows version, power supply and video card. What are you doing when the BSOD's happen?
Minidumps are:
KMODE_EXCEPTION_NOT_HANDLED
PAGE_FAULT_IN_NONPAGED_AREA
DRIVER_IRQL_NOT_LESS_OR_EQUAL
Ntoskrnl.exe
You have tested the memory and hard drive...