try leaving the monitor off while you boot windows. 1s your sure windows has started turn the monitor on.
if it comes on then you have a power brick problem in the monitor which isnt that hard to get repaired. it will cost you about 20 pounds to get it repaired
if it remains off and goes into standby then its the power circuit (capasiters and the likes) again not very hard to repair but will cost about 30 pounds for the repair. or you can send it back to dell if its less than 3 years old. as dell offer at least a 3 year warenty on most of there monitors.
Come HEX you know it aint the monitor.His system wont boot.