Vista 64 can't load with Memory Remap on.

[knector]

Hi, I am having some trouble to turn on Memory Remap, when I did it my PC booted up to a screen where I could choose to start normal or start a startup repair, my wire free keyboard could not change it so i put in another.
When I started normal it began to load for a sec and then I got a flash of a BSoD, then it booted up to the same screen again, when I turned Memory Remap off again it would still not boot, not before I had made a system restore from the Startup Repair, and then it was fine again.
I want this to be on because I just got Vista Home Premium x64, and can see it only uses 3262MB of my 4GB in the Task Manager, when I had x32 I could change Memory Remap with out any problems.
My thoughts is that I changed to a HD4850 vcard while I changed the OS, so maybe it could be a bad driver or hardware/bios settings. I don't dare to play with the settings to much course I'm afraid it suddenly won't boot at all.
System specs in profile.

CCC Version.
Driver Packaging Version 8.53-080820a-068908C-ATI
Catalyst® Version 08.9
Provider ATI Technologies Inc.
2D Driver Version 7.01.01.821
2D Driver File Path /REGISTRY/MACHINE/SYSTEM/ControlSet001/Control/CLASS/{4D36E968-E325-11CE-BFC1-08002BE10318}/0000
Direct3D Version 7.14.10.0612
OpenGL Version 6.14.10.7976
Catalyst® Control Center Version 2008.0820.2135.36847