Disk Boot Failure - Suggestions?

After having my system running smoothly for a year, I have twice (in the last couple of days) got a "Disk Boot Failure" during powerup. In both cases, if I hit the reset button, the machine boots normally. The only recent changes I've made are as follows: Installed a new audio interface card (Delta 1010LT) about 3 weeks ago. Have had no problems. Installed two pieces of audio/recording software. One of these programs is a little buggy and occasionally crashes or locks up the machine. But those were also installed 1-2 weeks ago, and the failure occurred for the first time 2 days ago.

I'd be interested to know a) what tests I should perform, b) what the most likely culprit is. I am not sure if the two times that this occurred on startup were consecutive startups, or if it was like 2 out of 3 - so it's not clear if it's intermittent or not. I'll do some more experimentation with that later after I've backed up some of my data.

Thank you!!!

My system is as follows:

Athlon 2700XP

SOLTEK SL-75FRN2-RL Socket A (Socket 462) NVIDIA nForce2 Ultra 400 ATX AMD Motherboard

Main drive: WD-80GB Serial ATA

Backup drives: WD-80GB IDE, Maxtor-10GB IDE