Question : Problem: Two tone alarm signal as the screen goes blank  -  what's wrong?

System: VIA Technologies Inc KT400-8235
Motherboard: Biostar M7VIT Pro
Processor: AMD Athlon XP 2500+ 1.8 Ghz
RAM: 512 MB DDR-SDRAM PC2700
OS: Windows XP SP2

Two days ago my computer powered up normally until reaching the desktop whereupon it powered off abruptly and a strange two tone beep alarm sounded from the MoBo (like an ambulance siren).  It continued for a few seconds even after I pulled the plug.    After a pause I tried to boot up again but got the warning tones right away.

What is this?  ......  PS failure,  Fan failure, CPU or Motherboard problem?

With the case open I notice that when I hit the power switch the CPU fan twitches but does not run.  I removed the fan and cleaned it as well as removing a lot of dust and fluff from the heatsink.  I tried a new fan with the same result.    Now I suspect the Power Supply but I am wondering if it is time to replace this 3 and a half year old system  -  would rather not if the problem isn't too expensive but I don't want to spend $90 - $120 on a new power supply if the cpu or mobo are fried

Answer : Problem: Two tone alarm signal as the screen goes blank  -  what's wrong?

The alarm code you are hearing should normally be short and long beeps. If it really does just sound like a "warbling" ambulance type tone, that normally means overheating. But if the PC won't start up at all, it's unlikely it's overheating, since it won't even turn on. (To test, try leaving it off for a few hours, then turn it on.. if it still won't turn on, then I'd say the first thing to check is the power supply)

You can pick up a cheap 350 watt power supply that should be fine for an older PC like yours for around 30 dollars. You could find a place with a no restocking fee return policy (like fry's electronics) and then try it and see if that fixes it. Power supplies dying after a few years is very commonplace.

As far as the age of the computer, it is definitely old and it would be a good time to replace it, BUT a 2500+ isn't THAT bad either, depending on what you're using it for. For cutting edge gaming, it would be a disappointment, but for web browsing and older games and such, it would be just fine.

If you've been thinking about upgrading anyways and you have the money, new computers are fun. If you'd like to save your money, I'd try a new power supply first...

If that doesn't do it, then it's likely the motherboard or cpu, at which point you'd probably have to do a new PC anyway just about.