my windows starts up as normal but on the desktop the screen goes blank,also it wont start in safe mode so i cant sort it out.is this a major problem

see if you have two adapters installed maybe the monitor is looking for 2nd adapter instead of the one your using... (possible solution): boot to CD. and reinstall/repair your version... also seen it happen when 1st monitor was shut off and 2nd monitor (very large screen) was used to watch a movie....