Harsh truth:
This PC is now pretty much e-waste. You've had a few years out of it (I guess?) which for the price you paid is probably pretty good.
Time to replace. You can go used if money is tight. You can probably pick up a used 24" monitor for ~2000 THB (maybe less!) and an ex-business Lenovo, Dell, HP etc. PC in a compact case from Shopee, Lazada etc. for perhaps 6000THB. That'll be significantly better than what you have now. Make sure it has at least 8GB of RAM and 256GB SSD. That should keep you going for a few years with the potential to upgrade after that.
Use an external hard drive (a branded one, Toshiba, Seagate, WD etc., not the trash one from Lazada above) or a USB flash drive to copy any important files from the old PC to the new one.
It would make far more sense to do this now rather than waste any more time or money on this device.
My 2c!