Try it on another PC to see if it stll has the same problem then open it up to check the power supply section, look for bad caps with bulging top, look for burnt marks on the PCB. Post back what you see inside so we can guide you further. See example of failed monitors due to bad caps: http://s807.photobucket.com/home/budm/allalbums

Disconnect vga signal cable of monitor and keep power on monitor will show the display that no siglnal check the signal cable then monitor is ok fault lies in the cpu check the ram by disconnecting ram from motherboard listen the beep if contineus beep is heard then motherboard is ok ram is faulty replace the ram problem will be solved