Graphics glitches and lag when maximum memory is unchecked! HELP!

Since so long i had this problem,so im asking everybody here if they have a solution!

So i have 4gb ddr2 ram with a 64bit OS
I want to use all 4gb but when i do that EVERYTHING lags and glitches!
I need to go to msconfig>boot>advanced options>and then need to check Maximum memory
Then i restart and when i go to system installed memory shows 4gb(3.26gb) and with that everything is fine
But i want to use all my memory so games run better! it bothers me really hard
Here is my dxdiag,PLEASE HELP!
DxDiag.txt

A part of the installed/system RAM is automatically assigned to onboard/built-in video/graphics adapter. The minimum RAM for 64-bit Windows is 2GB, double is much better but with video editing, large spreadsheets and databases more is even better. And it may be necessary to follow Windows Help on Virtual Memory/paging file for 1.5 times the physical memory or more if programs need it. Or for that program you might check out ReadyBoost and plug in a USB Thumb/Flash drive or SDHC card if you have a card reader in the computer.

I didn't catch the nVidia video in your Specs but would wonder if there is an onboard adapter on the motherboard that hasn't been disabled when the card was added.

Ok,is there a way i can have all the ram available,in System its Installed memory 4.00 GB (3.24GB Usable) I want to use all and if i uncheck it uses all! but everything glitches and freezes

Can you get the make and model number of the motherboard in that MaxData computer?
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