I just got an AMD Sempron 3400+ (socket 754), as I got a refund for the dead Athlon 64 I had and they didn't have any more of those. Anyway, I'm using an ASUS K8V-X SE motherboard and after rebuilding the system and trying to power on, all the happens is the 3 keyboard lights (Num Lock, Caps Lock, Scroll Lock) flash constantly. The CPU fan doesn't spin at all, even though it's connected to the motherboard. Both the 20 pin and 4 pin power connectors are connected to the board. I've taken the memory, graphics card and IDE cables out of the board to see what happens, but nothing other than what is described above.

Any ideas? I seem to have had bad luck with Athlon 64/Sempron CPUs and I want my desktop back .

Thanks.

Make sure the PC speaker is connected to be able to hear any error beeps.
Try booting it with no memory. The board should beep constantly. If it doesn't beep and just basically sits there, it is probably your mainboard.
You might also want to try a different power supply. Getting lights and a response from a power supply doesn't mean it is actually still working.

Nope, no beeps. Edit: and yep, I tried both with and without memory.

God, I've had three motherboards and one was faulty. It's too late to return this one now. Grr .

I'll try the PSU with my Socket A board, because it was working with that and I've hardly used it since (well, I haven't been able to).

Great, more money to spend on another PSU if this one's not working.

Thanks.

Every kernal panic I have gotten, and I have a alot, has caused the numlock and caps lock led`s to blink and keyboard and mouse to freeze, thats probably what it is.

Yep. Happened to me also. Kernel panic (old 2.4 series on Debian) did just that : blinking and blinking for caps and numlock. Don't give up on your mobo yet.
cheers