Extruder (hotend) always on!!!

[trypakias]

Board : Geetech GT2560, with AtMega1280

History :

I was printing normally for 2 months when it suddenly stopped printing. First issue was the PTFE teflon that guided the PLA to the nozzle.
I cleaned the nozzle and replaced the PTFE. I managed to get 2 more perfectly made prints.
After that the nozzle was not starting to heat after the bed reached the right temp, even when I forced it through prepare mode. I had to disconnect the hotend (nozzle) from the board, wait till the led switched on and then connect it. I noticed that the led was not switching on normally, it's like it was gradually switching on, that's why I was disconnecting the nozzle's resistance till the led switched on normally. I managed to get 2-3 normal prints after that. Then it stopped heating again.
I checked the wiring, measured the resistance, checked the fuses, the mosfet, everything worked perfectly, seemed like it's a software-programming issue. I used the command preheat PLA from the menu and then it started heating again, but it never stopped heating after that. It reached Maximum Temp (giving me an error) where I switched it off.
I tried flashing it with a new firmware (the one I got from the forums) but no luck, I even got an USBASP (ver 2.0) to flash the bootloader too, thinking that may be a software issue but no luck.
Now every time I switch it on, the led over the heater connection stays on and there is always current at the pins, when I try to connect the hotend's resistance it doesn't stop even when it reaches the max temp.
Any ideas on how to hard reset it, firmware upgrade it, or work things out?

[William]

It uses to be a firmware issue that can not recognizes the max temperature, you could try updating the firmware via Easyprint.