Oh, you're using the wrong OS, 32 Bit can use only a max of 4GB approx.... irrelevant of how much extra RAM is put into the rig. If your BIOS show all 8GB you will still end up using less than 4GB in a 32Bit OS.
To utilize more than 4GB of RAM you need to have a 64Bit OS installed.
Yes, Only 3GB of RAM is what your system is capable of using from the installed 8GB.
That is the rule of the 32Bit structure, it can't read beyond a certain number of zeros ..... so you're stuck with it until you change your OS to a 64Bit version.