Sometimes my computer stop working

A couple of years ago my computer crashed. I did reload everything and it is working ok. Now some of the functions dont work like internal dvd/cd player does not play the dvd's at all. Some of the games work not flight sim. I reload flightsim and the computer freezes up.I use to play dos games on my computer and I cant get that to work. I cant get the computer joystick to work at all. Can anyone tell me do I need new or more memory? I am still using 512mb with Win98se. Yea I know I need to update to something better but right now money is tight and I would like to see if I can get this fix.