Blank screen on monitor but fans work

Desktop computer was not used for a couple of months due to absence from home. Came back and wanted to make use of the PC, discovered that the Processor fan is working, Power pack indicator at the back of the System Unit is working, DVD Drive opens and closes when pressed, Monitor is blank, power indicator in front of the Unit doesn't come up.

Have removed and cleaned the RAM, yet no improvement. No beeping sound when RAM is not in the PCI slot. Keyboard and mouse doesn't come up.

Please what could be the possible cause?