fsx sp2 crashes computer

I have a new computer with loads of everything, which has been working properly with fsx, sp2 for a couple of months.A few days ago I reinstalled Windows from the very beginning (loosing all documents and applications of course).First thing I did was install fsx, then sp1, then sp2, then uninstalled sp2 to TRY to install a bright new Acceleration pack (as this last installer tells you to unistall sp2). I say "TRY" because as soon as the installer starts I get a Blue Screen of death with a "Memory Management error".I have tried installing loads of aplications since this error, and belive me none has given any problem at all, its just Acceleration Pack and curiously the sp2 too.I have a Windows Vista 64bit with 4 gb RAM. I have tested the RAM with utilities, also no virus found, I also tried to clean the RAM terminals and changed them position, try one by one, but still get the blue screen.