Comb through device manager and see if you have any conflicts. Make sure you've got the latest drivers for everything. Please post system specs and power supply rail volts/amps. This could be a lot of things.
Abit IS7 - 2.8C @ 3.4 - Mushkin PC4000 (2 X 512) - Sapphire 9800Pro - TT 420 watt Pure Power
Samsung 120gb ATA-100 - Maxtor 40gb ATA - 100
Sony DRU-510A - THAT'S MORE LIKE IT!