Blank screen

Ok my PC shut down due to fan issue. So I cleaned out all the dust and muck after disconnecting the PC from the power source, keyboard, monitor and mouse
I turn the PC back on after reconnecting everything
The tower sounds like it’s running and the fan is running.
But the monitor is blank
And yes I made sure I turned the monitor on
Shows something like monitor is not connected to PC
But everything is connected as it was before
Any ideas about why the monitor is not connecting and how I can fix it?