Flashing monitor light?

My monitor light is flashing on and off when I boot up my PC and also when the PC is off.
It's done this before but I can't remember how I fixed it.
Any ideas people?

 

First thing to check is that the monitor cable is connected correctly. Power down the system and unplug the monitor cable from the system. Look at the end of the cable and check for any bent or pushed in pins. Reattach the cable to the computer and power up the system.

HTH

 

Ok I fixed it thanks for the reply. It was actually just a heatsink on the cpu that was on the wrong way. And the RAM was also not in the correct slots.

 

OK. Glad it's its all working now.