Memory Management - Blue Screen - Vista Enterprise 64 bits

In the last monts my computer was give me a blue screen (sometimes)
error with the next message "Memory_Management" I supossed was the RAM I
change it and test each memory and still the error, I change my Video card
too. So my computer have this specifications:
Core 2 Duo 1.80 GHz
3 Gb RAM
1 Gb Video
Vista Enterprise 64 bits
I have all the updates until today
The system recovery y send the error, but till now no solution.
The error show up sometimes when I'm starting the computer, so it can't be
an program ran. I was thinking and I didn't have this problem early, this
began when I installed some update but I don't now wich one.
Now I'm trying with a new install with SP2 directly. My question is if an
update can gave me this error ?
Regards.