I built a PC two years ago and i just cleaned it recently. I discovered that the 4pin plug which goes into the motherboard melted a little (24pin plug also turned a little brown but barely noticeable). I didnt pay much attention and plugged it back.
Everything was fine untill recently:
-My PC restarted itself after a 20-30 minutes everytime I turned it on.(Everything booted and it worked fine, I checked the HDD, CPU and the Video card, I didn't notice any problems)
-After a while it restarted and the leds were dark but the fans worked, nothing showed up on the monitor. I restarted it and then everything was fine again, my OS booted. I turned it off and took a look at the 4pin plug and it was melted.
Here I stand completily puzzled what to do.( I could go to a an expert but i think he just say that I should buy another power supply and he wouldn't check anything)
My PC specs are the following:
-Nvidia GTX 460
-Intel quad core q9400
-Samsung HDD HD103SJ 1terrabyte (SATA3)
-P5P43TD ASUS motherboard
-Powersupply: HKC USP5565 2.2version 565W (it was a really cheap one, around 50USD)
The orange wire on the 24 pin connector should be the +3V conductor. The wire on the 4 pin that's fried also looks orange, but must be red, because that would be the +12V conductor. Either way, it is a sign of a poor connection that was arcing, or something on the board that was drawing way too much current. I would doubt the latter. The PSU is unsafe to use and should be properly disposed of.
The 24 pin header on the board 'looks' OK, but the 4 pin is questionable from what can be seen in the pic. If I had to guess, I'd say the cheap PSU had poorly manufactured connectors that caused arcing due to poor fit. Or perhaps poor wire-to-pin connections. You could try a new PSU and see if it fixes the issue. Ideally, you'd want to replace the board too. But if that is out of the question, try the new PSU first.