1) Go into BIOS, usually under "PC Health" or something similar and check the power rails to see if the +12volts is actually +12 and so forth. They s/b within 10% of stated voltage.
2) Better, download free program Motherboard Monitor 5 (MBM5). Install and run the "dashboard". It will display all the rails and as you work on your pc you can monitor the flucuations to make sure they are within tolerance.
I understand you can set MBM5 to monitor in increments of 5 seconds and make a report, so that when problems happen you can call up the report and see if power started to flucuate badly causing the problem.
I think you can also use a multimeter to check the rails. But I'm guessing if you had one of those you wouldn't be posting this question
Barton 2500+
Abit NF7-S v 2.0
Maxtor 60GB ATA 133 7200RPM
512MB Corsair Twinx 3200LL
9600 Pro
Enermax Noisetaker 420 watts
Win98SE