I have an old Pentium 4 in a SFF. The ranges on the pc were 166 to 350 in the BIOS screen. I set it to 260 and now when I turn on the computer, the P4 HT screen never appears. If I load a cd into the drive it spins and then nothing happens. I tried loading the bios set up cd, kill disk, ubunti and still it's not booting. Did I kill my P4 by trying to over clock it or is there a way to get it to boot up properly again?
Use the Clear CMOS jumper on the motherboard to reset it to defaults.
Normally this is 3 pins, and the jumper will cross 2 of the 3, you just move it one position over (so instead of pins 1-2 its now on pins 2-3). Wait 20-30 seconds, then put it back in it's original place. Power up the computer.
95% sure your machine will start again.
Chances are you've exceeded the max clock speed at the selected VCore, raised the PCI bus too high, or set the memory frequency too high (or a combination) by raising the front side bus by a margin of over 25%. Before raising FSB it's required that you watch or lock those values.
Older P4 boards don't have as many overclocker friendly features as the new boards, hence why it probably just sits there doing nothing.