With regards to the RAM, your pc could be detecting only one 512MB memory stick now and, like Eric said, 32MB is shared with your onboard graphic card. That's why you can only see 480MB.
To find out if any of them is KO, first use an eraser to erase/clean up the pins of the memory sticks. Then boot up the pc with only 1 stick in it. If you can hear several continous beeps during BIOS startup then most likely that particular stick is kaput.
Check too that there's nothing wrong with the memory slot with a torchlight. Sometimes foreign object in it can also cause you probelm.
BTW, memory sticks come in both single and double-sided types. Being double-sided, the latter is thicker.