What is the cause of this?

[Obsydion]

All I did was replaced a13,5gig IBM(7200rpm ata66) hard drive with a 30gig IBM(7200rpm ata100) hard drive, and MBM5.03 stop functioning properly. Indicating a CPU temp. of between 37c-38c constantly, weather idle,or under load. If I load Asus Probe then MBM function as before with readings between 29c-38c, respectively. I reloaded the programme several times to no avail. The system is a P3 800/100 cCo overclocked to 1gig. Using a Asus CUSL2 Mobo. Alpha PAL6035 HSF(Delta) with artic silver. Can anyone give some indication as to the reason behind this strange occurrence. I also reflashed the BIOS, but it did not change anything. Thank.