2 way a cable can burn like that :
- short circuit (that could be short either with the cable itself or on the VRM circuit of your mobo, but now your PC can work normally, short on VRM can be rule out)
- Over current, a cable is rated "safe" at a certain amount of current (Amp), if over the rated value, then it will heat up until it burn and melt. Do u overclock your PC ?

Anyway, why u decided to use an 4 pin extension on the 1st place ?

Hi guys. So I unplugged my PC for about a week (outstation). When I come back home, it won't turn on, the power led was on and fans were spinning for half a sec then it just shuts off.

I opened the case. Basically reconnecting everything, and it started again normally. I thought it was just the mobo power cable connection. I even game on it for a bit this morning. Suddenly, just after finished gaming (game closed already), the pc shuts off by itself, and tries to start back up and fails again in a loop.

Any ideas?

Im currently facing the same prob this morning