Is my mobo dying?

So my computer is acting funny. It keeps locking up for not apparent reason, and I think I have eliminated all the components minus the CPU and motherboard, and I do not really know how to go about diagnosing problems in them. My basic question is how to diagnose motherboard problems.

My computer:
The base is a Dell Dimension 4700, but the only things left from the original computer are the motherboard, case, and CPU.
CPU: Pentium 4, 3gHz
Motherboard: Stock Dell Dimension M3918
Chipset: Intel 2580rev4
Bios: Phoenix V1.10 A10
OS: Windows XP

And just in case I have 3gigs of Crucial RAM (2x 1Gig + 2x512), an EVGA nVidia 9800 with an aftermarket cooling system, and a Raidmax 730W power supply and I just installed (about two weeks ago) a Seagate Barracuda 7200.10 ST3250410AS 250GB

The Symptoms:
These are kind of bizzarely specific, but it happens this way every time.
-My computer starts up just fine, and nothing at all seems fishy.
-Then, after a seemingly random amount of time my (wired) internet connection dies and cannot be restored all it says is "Cannot connect!"
-Soon after, my active window freezes, and does that thing where if you drag other windows over it, it goes blank or captures the trail of the window. Nonetheless, I can still move my mouse, I can make other windows active and then do things like type in them.
-But as soon as I do something like right-click or open a menu or try to bring up the task manager, the entire system locks up.... except my mouse. My computer seems dead at this point. Except for my fans ans power supply, nothing is making any noise at all. It will stay this way indefinitely, or sometimes my motherboard will let out a continuous beep until I shut everything down.
-This will happen even if I am doing nothing at all, but will -not- happen if I leave windows in the login screen.
-I have run memtest and found nothing, and have reseated all the memory. I have updated my BIOS and all the drivers I could think of. I ran a virus check, and looked specifically for the latest worms. Right now my computer is running chkdsk on my hardrives.
-I have never once gotten any sort of error message about anything, and, aside from the lock up, there is no other performance decrease.

I told all of this to a friend who is better than I am, and he said that it sounds like my mobo is dying. What do you think, and how can I test to see if there is anything wrong. Thanks.

 

This could well be an overheating problem, check your CPU fan is functioning 100% check your temperture control in bios, the continuous 'BEEP' points to overheat, have you defluffed recently and is there plenty of air flow in the rig. Is the cooling system for Nvidia Graphics working OK. Try another PSU as power failure could also cause this prob.

 

Thanks for the quick response.

Overheating was my first thought too since it seemed to be time-based, but both my GPU and my CPU hover at around 40-45 degrees at idle, and the problem can occur while idling as well. The My power supply is only a couple of months old, but I'll switch it out later this evening when I have the time. Thanks for your suggestions.

 

I'm not entirely sure it is a hardware issue,so you might want to hold off on purchasing a new power supply. I ran into the same problem over the weekend, but have been unable to figure out what is causing it. However, running the computer in debugging mode seems to be working fine. The same exact problem has arose among others over the last few days, which is why I think it is too much of a coincidence to be a hardware issue. Here are some links to other forums that you can check in case a solution is posted in the future.



http://www.overclock.net/intel-cpus/486062-windows-xp-freezes-1-continuous-beep.html

http://forums.pcper.com/showthread.php?p=4364665#post4364665

 

Did a reinstall and that fixed it. More info over at the overclockers page.

 

A fix has been found for this virus:

http://rootrepeal.googlepages.com/RootRepeal.zip

Finds an infected MBR file, once removed, your computer stops freezing.