start with bare minimum - vid card, ps2 keyboard and mouse, 1 stick of ram(you didnt specify if you had qty 1 512 mb or qty 2-256mb), and hard drive only (preferably ide hard drive instead of sata). pull out any network adaptors, sound cards, etc. disable onboard devices not being used.
set bios to 'failsafe' values and disable all items not being used.
test ram with memtest86.
if you must use sata drive - use the drivers, etc that came with it - load em up. (no details as i have never used a sata drive with win98).
check the 'device manager' for any yellow exclamation marks, etc - anything indicating some hardware is missing drivers, errors, etc. - correct them.
give us a progress report.
if you have specific details on the error(s), post them.
gooooooood luck