The monitor will always say 'no signal' until it gets one from the computer so it is possible it will always say this for a split second after youve switched on.
If its switched itself off ever since you bought it then its probably a hardware fault, take it back to the shop if its only 6 months old its still under warranty.
If its started doing it recently it maybe a software problem, try system restore back to before it started, or reinstall windows - should have restore disks with computer - NB. All your data will be lost.
www.diypcfix.co.uk
www.diypcfix.co.uk
August 2007