I accidentally connected a psu wire to the sys fan header in mobo, after switching on my sys it switched on for a sec then turned off , then I removed the psu wire from mobo and switched my sys again, it started working again but I am worried that if something happened to sys fan header or something else? Is my sys completely fine after doing that mistake?
You will find out once you use the system for a while if it's fine or not. There is no way to know past a wild guess if anything was damaged if system is working now. How do you even plug in a PSU power cable to a fan header? They are very different connections.