My PC has for no reason started to power down 5 seconds or so after I switch it on at the front. What's wrong and how do I fix it?

I had got overclocking errors recently.

Are you overclocking your chip? If so, try running it at it's native speed. You may be overheating the chip fairly fast and the motherboard's thermal limits are being reached.

well he cant change his speed since it shuts off. try removing ur cmos battery for 20min, then but it back in and start back up. if you have a cmos jumper, it would be even easier.

I managed to get it switched on, but it usually happens again. How do I turn off overclocking on a Pentium 4?

from the bios. there should be a function button that allow you to reset ur bios settings to defualt. and resetting the cmos always works like i already said...

from the bios. there should be a function button that allow you to reset ur bios settings to defualt. and resetting the cmos always works like i already said...

Make sure the fan is spinning.

And check your cooling paste too ...

...also in BIOS check the power voltages, if they are jumping all over the place... It could be sending spikes of power to the CPU, making the motherboard think that the CPU is trying to be overclocked.
If this is the case, you need to replace you Power Supply. But, Test the above listed first.

~Dave