Did you build this PC or did you get a prebuilt? If you built it yourself, it should be quite easy to troubleshoot. Firstly remove one stick of RAM and see it the system still works and shows ~3 GB. If it works, remove that stick and insert the other RAM stick to test if the system works and shows about ~3GB. If one of the stick works perfectly and the other one shows a lower RAM, the one which shows the lower RAM is likely faulty. If both of them work, try inserting the RAM into the appropriate dual channel slots and perform a CMOS reset. If it does work, go in your BIOS and adjust the RAM frequency to what the manufacturer recommends e.g. 2400 MHz or 3200 MHz.