18 GB UDMA\66 lost clusters frequently

I have an AMD K6 IBM Aptiva with 128MB RAM. I’m running Win98(2nd Edition)which I update regularly with Windows Update.I just purchased an IBM 18GB hard drive (UDMA\66. It has 2 MB buffer at 7200 RPM. I partitioned it with Partition Magic v5.0 andBIOS settings in “AUTO” and “LBA” selected. All works fine, however after a day of Internet and running various other programs, my PC locks up. I have to cold reboot, run “Norton Disk Doctor” which results in 300+ lost clusters or chains. I fix the problem and I’m good to go for another eight hours. My question is: why is this happening and what steps can I take to prevent this from happening?