An issue with over 2Gb RAM under Win Vista, A8N-SLI SE Nforce 4 SLI Options

[FacelessXXL]

Hi there!

I faced a strange behaviour of my brand new ASUS A8N-SLI SE, under the Microsoft Windows Vista Enterprise build 6000 (RTM). It started, when I bought and installed 2 DDR400 1Gb memory modules, which replaced 512Mb ones. So, it became 2x512 and 2x1024 Mb (3Gb total). I did some loops with MemTest, as I usually do for new memory modules. Everything was OK, it started in Dual mode without any errors. Also, Vista didn't create any warnings about the new hardware - it was successfully identified as "3071 Gb" in "System" menu.

So, everything went fine, untill I inserted a Flash disk into USB slot (as I did many times before). Nothing happend, as it was no disk at all. I looked in device manager and found out that "Mass storage device" is enabled, but not listed in Disk list, and every action to that "Mass storage device" (stop or update driver for ex.) results in several minutes of waiting, untill I remove it from USB slot. There were some errors in Event Log during this operations "Controller error" (for flash disk) and "Logical disks service error". Situation was the same with every Mass storage I have (incl. Card readers), but everything was fine with other USB devices (printer, mouse etc.). And there are no other errors, only with USB Storage.

Vista also works fine with every combination of memory (2x512 or 2x1024) but it is impossible to make USB Storage work with both this sets working together.

I tried everything I could, including fresh install of Vista on formatted drive, different memory settings in BIOS, etc. No result. Of course, I set all the timings manually. I even tried to set them to the worst (in the mean of performance), to exclude the possibility of "bottle-neck". I also tried all possible combinations of memory units - it doesn't make any changes. If i set more then 2 Gb of RAM (1Gb+1Gb+512Mb or 512Mb+512+1+1) I loose my USB flash drives. Everything else is safe and sound, in all sets: 512+512+1 or anything below 2Gigs... I checked IRQ's, conflicts - there are the same OK's for every combination. 3 loops of Memtest - 0 errors. Several 3Gb files archived with RAR - no CRC errors.

Maybe, I can get some ideas from the specialists? Is it known issue?

ps: all works fine under XP SP2.
pps: AXP 64 3700+, 2x512 Hynix DDR400 + 2x1024 PQI DDR400, ASUS EN7950 GT, 2xSeagate 7200.10 (Raid 1) SATA2 + Samsung 160 Gb SATA1, NEC 3500 DVD

Thank you for help,

Regards