try key DEL or F1 or F2. depends on your BIOS. can you write me please more about your computer/laptop? i`ll try to find it for you, exactly for your model of computer. if you have kit computer, send me just info about your motherboard.
info about your computer you can see in programs like HWinfo32 or Everest or other ... (recovery BOOT CDs, ...).
If its your problem 3GB RAM in 32bit Windows and you have in your computer physicaly 4GB then you need 64bit OS.