Hi,
The first thing to check out would be your BIOS the latest version is F11 and shows that CPU compatibility has been improved. You can download it from here:
http://www.gigabyte.com/products/product-page.aspx?pid=3266&dl=1#dlIf you are not sure how to flash BIOS using the QFlash Utility here's a quick how to for you:
The safest and best way to flash BIOS is to use the QFlash Utility.
There are a couple of steps to take before updating BIOS the first is to download the latest version from the web. Be careful that you get the right BIOS version for your motherboard and in particular check out your motherboard's revision number prior to downloading.
Once you have downloaded the correct BIOS Unzip the folder using WinRAR, 7Zip, Winzip etc., Save the folder to your desktop for easy access.
You will find a USB Stick is the best way of flashing BIOS so make sure the stick has been formatted in FAT32. Next copy the BIOS folder, that you have extracted (and saved on your desktop) to the USB Stick.
Leave the USB stick plugged into your PC and re-boot. As the PC starts up press the "END" key on your keyboard (you might have to press the "END" key several times during start-up before you see the message regarding QFlash, this is normal so don't worry just as you would the "DEL" key for entering BIOS). Don't worry if you enter BIOS instead as you can get to the QFlash utility by pressing the F8 key on your keyboard from the BIOS Home Screen.
The PC will enter the QFlash utility and you need to locate the folder on the USB Stick and then follow the on-screen instructions.
When the BIOS update is complete re-boot the PC and go back into BIOS.
Load optimised defaults, save and exit.
When the PC reboots you will see that the new BIOS is installed.
NOTE: Sometimes the latest available BIOS is a beta version and although it will work you might find some things are missing and overclocking, for example, might not work properly. If in doubt I would recommend that you do not update to BETA unless there is a noted "fix" for an issue that you are facing or if advised to by Gigabyte.
Hopefully the updated BIOS will solve your CPU problem.
If you are using the 32 bit version of XP then you will not see all 4 gig of RAM normally you will see about 3.5 gig, this is normal and is due to the limits of a 32 bit system.
So where, you are asking has the rest of your memory vanished to? As you are using the on-board graphics a certain amount of your RAM is taken for this, usually about 512 Mb. (The amount can be adjusted from within BIOS but is really best left at its default setting.) and some is reserved for system use. That is why you are only seeing 2.75 Gig.
Hope this helps
ATB