when you biuld a system you should put it togeather piece by piece.
that is, put the motherborad, cpu, ram (single stick), video card, hard drive, floppy, cd-rom drive, mouse and keyboard and see if it boots up. If you are missing something , or something isn't working it should come up on the screen, if the video card isn't working then it should beep.
If you have some old parts keep them close by just incase something doesn't work, eg, video isn't working, swap it with another and see if it works or not. This is the only way for sure that things work or not.
Once you have this basic system set up, install the opertaing system and then add each add on card etc, installing one by one. eg install the sound cardm then network card, modem, etc etc making sure each works properly before you install the next one.
Take your time and double check everything, and you should be fine.
