"NO SIGNAL" for no reason?

For some reason, my computer has recently been on the fritz. I will just be sitting here, and my monitor will go black and "NO SIGNAL" will pop up on the screen. This also sometimes happens when I am playing the game Elder Scrolls Oblivion. I have automatic restart turned off, so I'm not sure if it is trying to restart itself as well. I have no idea what would be causing this. I thought it may be a bad power supply, but I replaced that with a new 480w supply, a complete reformat, and I'm still having this issue. I ran SiSoft Sandra, and the only issue that I saw was this error:

Warning W235 - Processor Vcore less than rated minimum. Unless the reported value is incorrect or the processor is a different type that is not correctly detected, the voltage is lower than it should be. If you’re under-clocking the processor you may have pushed too far.

I have no idea what that means, or if it could be causing this.

Here are my specs:

Gigabyte K8N Pro main board (using onboard sound)
AMD Athlon 64 3000+
1GB ram
NVidia GeForce 6800GT
Windows XP Pro sp2

ANY help would be greatly appreciated as this computer is used for a lot of work.

Thanks in advance....

 

i dont no but all i can tell you is that , restore the bios settings to default and c what happens

 

Could it be the monitor that's causing this, or is it more likely a hardware issue? The computer lost signal again sometime last night, and doesn't want to boot up today.