Monitor goes blank randomly

I have a Intel core 2 duo pc.
DG41WV, (1+2) GB ram, No graphics card, no game installed. XP & 7 32bit dual booting. 500 GB hdd.
My monitor goes blank randomly. Power light blinking. Keyboard light goes still. No keyboard switch works. But my mobile (attached with data cable for network purpose) does not show that net connection is detached. I have to whitch off power supply. The problem happens while not surfing net or surfing net both the occasion. MoBo light remains on. CPU fan remains on.
1. I tried with using good quality UPS.
2. I tried with different rams.
3. decreasing system load.
4. Checking temperature with speccy software (35 - 40 degree)
5. Used various antivirus.
6. Installing XP only, Seven only, XP & 7 dual booting.
7. Changed monitor.
8. Updating MoBO drivers.

The problem occurs randomly. sometimes 7 or 8 hours continuously with no problem, sometimes within 2 / 1/ half hour problem arises. Sometimes at the time of booting problem arises.

Can anybody help me pl. I am totally fed up.

Hi

Try the monitor on another machine...if it still does it...bin the monitor...

All the best Brett