It seems my filament is burnt when I use PETG I use the Cura; nylon default(recommended) settings for PETG. Upon my filament's box is written 200-240 for nozzle and 75-85 for bed. So I tried 245/80 - 220/80 - 220/60 - 245/60.

But I got same result as you can see in the pics:





My printer is PrusaI3 (actually a chinese kit that I assembled it myself). Also I had good print results with PLA before this. I was using 190/50 for PLA).
It looks like you have a clogged nozzle/hot end. I use 225°C @ 40mm/s for PETG with 235°C @ 30mm/s for the first layer.

If you print at 245°C, you risk burning the PTFE liner in your hot end. You really need an all-metal hot end to print at such temperatures.

It is possible that you have already damaged the PTFE liner, and this may be the cause of your problem. However, I would check for a clogged nozzle first.