Two-tone continuous beeping (like a siren) coming from mobo. Nothing shows upon powering up?

[Xpred]

Hey everyone. I seem to have a problem with an older computer of mine. I built this computer back in 2005:

Athlon 64 2800+
Abit NF8 motherboard
GeForce 6800LE 128MB AGP
2GB RAM
3 HDs: 200GB, 250GB, 250GB
Antec SmartPower 450W PSU (old)
Antec SmartPower 400W PSU (new)

Originally, the computer would emit a high-frequency sound when it was both turned and off. When the computer was powered on, this sound would lessen, but still be apparent. After about 2 weeks, my brother turned on the computer, and suddenly he could hear some sort of buzzing for a few seconds, and then the whole computer turned off. He also smelled some smoke. So I believed the PSU might have died (due to the high buzzing sound that was apparent 2 weeks before something ?fizzled? out) because nothing would turn on anymore.

I replaced this with another older PSU I found from one of my computers: an Antec SP 400W. I plugged everything in and powered the computer on. However, after 3-4 seconds, I hear a two-tone continuous beep that has one high and one low in tone. It sounds exactly like an old school siren. It is coming from the motherboard. There is no OS beep or BIOS screen. Just nothing comes up while the computer is powered on (all fans okay) and the two-tone starts. I quickly tried searching online and digging through my mobo?s manual. Online suggested something of overheating while the motherboard said nothing about error beeps.

I have tried taking out the motherboard battery for a few mins and putting back in. I?ve also tried resetting the CMOS jumper settings. I've also tried switching the RAM thinking it was bad RAM. But that's that?s really all I have tried. Not sure really what?s going on. I think maybe I fried something (CPU, possibly?) as the older PSU died and maybe took something with it? There is also another thing I noticed. My motherboard uses both the 24-pin ATX & 4-pin ATX12V connectors. When I remove the ATX12V1 (4-pin), the CPU would not beep anymore upon powering on. However, the same result still shows: no OS, no bootup beep, no BIOS, nothing on video/screen. I don?t know why this would be??

Any suggestions on what to do? Thanks.

 

[baddog60]

I had a bunch of motherboards that did this to me. It ended up being bad MOSFETs on the board. They would give off that same siren like noise. That said, it could still be your power supply. Those Antec SmartPowers have a lot of problems.

 

[Pantlegz]

I know my video cards do this when I forget to plug in the 6 pin power connectors. so it may be the psu not powering the connector or just not enough juice for the gpu.

 

[mpilchfamily]

Since the sound happens while the system is off then its a dieing PSU. Get a beter PSU and try things again. If you still run into problems then thats another mark for the Smartpower series of PSUs. They are known for killing other system components when they die.

 

[Xpred]

Ah, do you think the mobo is fully dead? I mean, everything turns on. All fans are running fine. The light on the mobo is still on when the "on" switch behind the PSU is turned on. Or maybe the "functional" part of the mobo has died?

 

[Pantlegz]

the only real way to tell is to replace it and see what happens.

 

[baddog60]

When I had the problems with the MOSFETs you could see the physical damage on the board. Just so you know the MOSFETs should be between the CPU and the IO Backplane. They are next to the rings wrapped with wire coil (Inductors).