my old pc was running 98 i tried to install an internal zip and a sound blaster card got a fatal error then rebbooted but now moniter is blank computer is on i can hear the hard drive

Start by pulling the Soundblaster card and see if the computer will boot. If that doesn't work, pull the Zip drive. A bad drive or card can stop the computer from booting. Also, check cables and video card to make sure you haven't moved them in the process of installing the other things. Make sure you haven't pulled cable ends loose from the motherboard.