My Pc Keeps Turning Off My PC Keeps Turning Off When I Restart It In The Bios I See The Word Overclocking How Do I Stop This?

My PC keeps turning off when I restart it in the bios I see the word overclocking how do I stop this? - my pc keeps turning off

OS Win XP Home Edition Version 2002 Service Pack 2
Pentium (R) D CPU 3.4 GHz
3.40 GHz 100 GB Ram
I have no idea what the outcome, I'm not a player, he is a computer at home.