Stable minus symbol with black screen when pc powers on

Hi

This C2Duo Pc is showing a stable minus symbol on left upper corner and black screen when it is powered on and it freezes here and somtines it show motherboard logo and freezes there what i have done is as follows

1.Changed RAM also cleaned old RAM with rubber.

2.Reseted BIOS jumper and CMOS Battery

3.Changed sata and power cable of HDD

Cleaned the motherboard with a brush

pls tell me what to do next?is the motherboard gone bad if yes what to do i cant buy new pc in these days

Thanks 🙂