when you right click on mycomputer go to properties ,what does it show there ,it could be you have onboard video, it will be sharing you ram.

it just shows the regular system specs with it saying i have 368 MB of RAM. How can I find out if I have onboard video?

right click on blank area of your desktop/properties /settings /advanced /adapter .it should tell you hetre if its onboard or internal type .and how much ram it is /or sharing

Well it says that it's DAC type is Internal and it also says that it's memory size is 128 MB. Is there anything else that can be using all my memory?

368+128 doesnt really add up to 512. Can you list the display adapter it shows over there? Go to Device manager, and under 'display adapters' let us know what it says there. If indeed it is an onboard display, and is using only 128 megs, it is possible your RAM stick(s) may be bad.

My RAM sticks may be going bad?? Lol, I hope not because I just bought it. But anyways under Display Adapters it says ATI Radeon Xpress 200 Series.

You can try memtest86 to check your RAM. Download an ISO-CD-image from www.memtest86.com , burn it and boot up from that CD. The test may take a while, but doing this is a good idea with a new computer or RAM upgrades.

But I've tried to find out why those 16 MB could be missing:
The ATI Radeon Xpress 200 is a highly integrated chipset, which contains a cost-reduced version of the ATI X300 graphics processor. This seems to use 16MB "core RAM", in addition to the "shared" memory portion for the graphics. There are 2 flavors of that chipset and one comes without the 16MB embedded core RAM, reducing costs further. With this one, I guess the "core" RAM is borrowed from shared memory, too.

Upgrade to 1GB RAM or put a decent PCI-e graphics card into the free slot, when needed.

Hmm..didn't know about the 'Core RAM' thingy. If that is the case, then I guess all questions should be answered now.

So there's no way to like 'disbable' the shared memory featured or do something to get the RAM back? If it's not then I guess I'll just have to upgrade

You can change the amount of ram used by the video in the BIOS/Setup of the computer ,by entering the bios when you boot the computer .and making the desired change to the video section of the bios .