HDD Intermittent Fail on Boot

My daughters computer is a Pentium III with 396 MB Ram and a 15 GB HDD running Win XP Pro. On startup it will repeatedly rtn error saying HDD fail. It will do this 3 or 4 times then will start normally. Sometimes it can take as much as 30 minutes of continually tryong to reboot before it kicks in. Replaced HDD with Known good one and got same result. Suspect built in controller on Moboard. Also suspect pwr supply. Any other ideas??