I am experiencing a issue with my new desktop pc. I am running a Gigabyte EX58-UD5 revision 1 with a core i7 920, 6 gigs of ddr3 ram at 1333 mhz and an hd 5870. When looking at my system properties, It tells me the following:
installed memory: 6.00 GB (4.00 Usable).
I assume by system properties, you mean from within Windows. Which version of the OS are you using, and are you using the 64-bit version? You need 64-bit Windows to use more than 4GB, so I'm guessing this is your problem.
I'm not on my Win7 machine now, but Win7/Vista should tell you x86/32-bit or x64/64-bit with the OS version on the system properties page. If you are using XP, you have to have Win XP Pro x64 edition.
Nothing else in your system should be limiting your memory usage, so I'm just guessing you have a 32-bit OS installed.
Scan through your BIOS. I'm not familiar with your board, but there could be a setting somewhere restricting the memory available to the OS. Look for something dealing with Memory Remapping (it needs to be enabled). Not gonna gaurantee it's in there, but it might be. Apparently I spoke too soon before, and this is a rather common issue with some boards and BIOS.