Lights start flickering on Luminous inverter when I connect my Desktop CPU
PCs, especially cheap PCs, have pretty big power supplies.  The &quot;850 watt&quot; power supply actually draws over 1200 watts.  It sounds like your PC is simply too much for the system.  It may be necessary to downsize the PC, maybe get rid of performance video cards, get a smaller power supply, etc.  One of the &quot;micro-PCs or a Mac Mini would be a great choice.
You can also look at a DC power supply for the PC, so it draws directly off your battery instead of needing to go through the inverter.