Memory issue

You never said what the problem was. The operating system determines the maximum RAM.

I want to use all of 4 GB ram instead of 3,24 GB. What about the 0,76 GB?
Is it reserved for something? I have no integrated graphic card.

If you want this to be solved, get a different motherboard. Think Gigabyte or Intel.

Typically, it's the 'usable' limit of a 32-bit OS, and/or onboard GPU and other shared memory devices.

ref - http://usa.asus.com/product.aspx?P_ID=RBA8CzWoopUlYRFZ

In your case with an x64 OS I would need to ask - do you also have a partition with a 32-bit OS and did you perform a clean install? i.e. critical 32-bit driver installed vs 64-bit.

BIOS:
Advanced -> Northbridge Chipset
/Change Memory Remap Feature {Disabled}

{I do not like GA or Intel MOBOs - period}

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