Showing 3.25GB USable Memory out of 4 Win7Prof64Bit

Hello.
I have self assebled desktop with following configuration-
AMD Phenom II X4 955 CPU
Gigabyte GA-MA785GMT-UD2H Motherboard
500GB SATA HDD
4GB DDR3 1333MHz Gskill RAM
PowerColor ATI Readon HD4850 1GB DDR3
600W PSU

I have installed Windows 7 Professional 64 Bit OS. After installation it was showing 4GB RAM. Recently, I noticed that it is showing 3.25 GB Usable.
Onboard graphics is disabled as dedicated graphics card is installed.
Why this is happening ?
Please help me out.
Thanks.

Run msconfig

Check under Boot, Advanced Options, make sure that maximum memory is checked and shows the 4,096MB of RAM.

Edit: And please, don't multipost the same question. I thought there was something wrong with my browser showing your topic as a new post and I answered twice....not realizing that it was a multi-post of the same question.

Run MSConfig,

Click on Boot, Advanced Options and check the Max Memory setting there.

Hmm not working

Thanks for reply.
Sorry for multiposting.
I ran msconfig and checked option Memory and value 4096MB and rebooted. After reboot, it was showing same 4GB (3.25GB Usable) and that option was unchecked.
Please help me out.

Hello,

Try downloading Speccy and see if it reports the memory correctly.

Also see this: The system memory that is reported in the System Information dialog box in Windows Vista is less than you expect if 4 GB of RAM is installed

Check in your BIOS for an option to enable memory mapping or something like that. If you recently upgraded your BIOS, it could have been reset to disabled.

Right click on the task bar, select Start Task Manager. Click the performance tab. Click Resource Monitor button. Click the memory tab. It will explain where it is and what is using it. Let us know what it says.
By the way, did U do a complete install or an upgrade install?