Windows 7 problems-monitors/power-up
 

I have recently started having a few problems with my computer. when the computer sleeps the monitor also sleeps but it does not wake up when I reactivate the computer through the keyboard.
I am also having a problem when the computer will not start after pressing the power button. I think that the problems are in some way linked as if I disconnect the power to the monitor and then boot the computer it starts normally.
Can anybody offer me any advice please?