My K8 NF9 won't boot. It just beeps.. Nothing on the screen at all. The Small heatsink on the motherboard has been running very hot lately. I have positioned a fan to cool it.

Disconnect the drive and try to boot to the BIOS (usually with F1, F2 or Delete key). If that doesn't work, try removing all cards from the computer (except a video card if the video port is not on the motherboard). If you can boot this way, try inserting back any removed cards to see what hangs it. Do you hear any beeps when the computer is booting (beep codes)?

Hardware problem:
* dead RAM
* dead video-card
* RAM not fully "seated" in its slot(s)
* video-card not fully "seated"
* dead fan on top of the CPU/heatsink.
* failing power-supply.

If there are no beeps, nothing on screen, all fans spinning, and hard drive spins up, chances are your motherboard is bad.

Could be a number of reasons:
The CPu fan and the PSU fans will come on, even though the system is not working. There is a possibility that the CPU has blown, you can check this easily by (carefully) feeling the heatsink after it has been running a while. A dead CPU will not use power and therefore not heat up. If after say 10 minutes of running, the heatsink is clay cold, suspect the CPU. Replace with another one, spreading CPU grease on the top before putting the heatsink back on.

A blown CPU will usually be indicated bu there being NO beeps from the system (see below)

If the CPU appears to be generating heat, visually inspect the board, look for blown or blowing capacitors (the small cylinder like components) on the motherboard, any that are bulging or leaking a brown residue, or have blown, will render the motherboard inoperative.

If these appear ok (they still may be damaged), unplug all components except the hard drive, and ram and video card, see if the system then boots. If it does, proceed to re-installation of each in turn, until the faulty peripheral halts the boot.

Listen for any beeps as the ssytem switches on these beeps describe the type of problem
(repost if you hear any beeps)

Remove one stick of ram and try rebooting, if it works, suspect the ram module, try the other and see if that makes any difference.

Failing that, your last recourse is to power the system off, remove the bios battery, replace after 2 minutes and see if clearing the Cmos "unsticks" the computer.

After That, suspect the motherboard is dead.

ok, you seem to have covered most of the normal trouble shooting procedures.. Now, you say it beeps when you take all the ram sticks out but does nothing when you fit ram. My first impression is that this is a ram issue. Maybe the ram is not compatible with the board or has been damaged. This can also be the case if the board itself is damaged. It could be that the i/o controller chip may have thrown in the towel and fitting ram causes the board to access this chip. No ram means control passes over to the BIOS error routines and the i/o chip is NOT accessed. Or, it could be both.. Try the ram sticks in another PC first. Static discharge damage is very common, even if you have the anti-static mats etc. I have mats, a wrist strap even my workbench is grounded along with my soldering station etc but I have still damaged boards through static discharge. I have also found that some brands of Ram simply do not work with certain boards so try the ram in another PC first !! Also, make sure that the ram you are using is correct and that you are NOT mixing different sizes or speeds. Next, make sure that non of the USB ports in the case are connected and that the boards own USB ports are not damaged as a bent pin in a port will always cause issues. Sorry that this may not be much help but as I said before, you are covering all the bases, the beeps without ram are making me lean towards a ram issue though..

Unplug the computer from the wall, hold the power button in for 1 minute. This will reset somehow the bios and remove any electricity left inside.If still doesnt work take a look to the cpu and heatsink

May be the CPU fan is going bad. I hope it is that simple.

have you thought about changing the battery on the motherboard, also checking that the fan on the cpu is seated properly with enough heatsink paste as both these issues will stop the pc from booting

The repeating single beep with a small pause (actually 3 Beeps a Pause) clearly indicates problems with RAM .Replace it ,your problem will be solved . As for connecting the 12 volt 4 pin connector all mobos are designed to sense the presence of this 12 volts and ONLY THEN TURN ON.

Do you have both power connectors from the PSU hooked up?

You need both the large one near the ram, and the smaller square 4-pin one near the printer port