Probably a hardware problem on your disk drive. If Oracle installed and ran OK, ignore it. If not, you might want to bring your OS up to date in case it has corrupted drivers and/or crack open the computer and see if the cables are all secure. Then, if Oracle still won't run, reinstall Oracle.
BTW, Oracle 9 takes somewhere between 5 and 10 GB to install unless you're good at deselecting options like the sample database. Make sure you have that much free disk space. This is another case where Oracle 10 is cleaner.