Interesting however there are a few things that come to mind. First off bro it might be time to upgrade....unless you are using some crazy legacy software that needs it
Next items, does your monitor turn off but you can still here the computer running? Or does the computer also go quiet? If the monitor just goes out but you still here the computer running could be the following:
1)Dying Monitor
2)Bad VGA Cable
3)Bad video port on computer
To test I would try using another monitor you know works as well as another VGA cable. If it still occurs you might be looking at a video port problem on the motherboard or if you have an old bgp video card that might be failing. If you have a custom video card and you are not using the motherboard video port you can always try to replace the card to see if that resolves it. Again you will have to good reason too pour money into this and I have to assume that you do.
Before I go further let me know about the above and we will see if we can get this resolved.