That is a common result of a poor mobo design decision - powering the CPU from +5 instead of +12 which results in very high currents in the +5 wires. When you have such high currents, all it takes is the right amount (a fairly low value) of contact resistance for heating to begin and from that point it's a vicious circle - one contact goes high-R, the current burden shifts to the remaining wires and another adequately high-R contact is found due to the higher current in the remaining wires, the load shifts more to the remaining wires (getting fewer and fewer), etc. Pretty soon all the contacts are getting charred and eventually the computer stops. Some pix I've seen on the AT Forums show the plastic to be entirely melted away on the PSU side - so you caught yours early with only mild charring. (Oops, I just noticed that the plastic IS entirely melted away around a couple of pins... Sorry!) On one of the machines I worked on, the +12 wire to one drive or another had its insulation melted off halfway back to the PSU from high contact resistance!
The high resistance could be due to several things: corrosion (are you in a high-humidity environment?), loosening of the female ATX contacts (PSU side) from thermal cycling exacerbated by the cheap contacts they are using these days, or even poor crimps on the PSU side contacts. Rarely is poor solder joints or some other issue on the mobo side a contributing factor - but that can't be entirely ruled out. You can test the resistance between the +5 pins and the copper they are soldered to using a DMM (digital multimeter) on the lowest scale - anything over 0.00x is suspect.
. So basically it is a bad mobo design choice (both AMD and Intel have recommended powering the CPU from +12 for a very long time as each wire carries much less current and for added stability) aided and abetted by corrosion and/or cheap contacts and/or poor contact assembly on the PSU side.
. I no longer consider mobos that don't have the P4-12V connector for powering the CPU.
. You could clean those contacts up (I use pipe cleaners (folded once for the male contacts on the mobo side) with good contact cleaner solvent like Caig Labs' Deoxit). And then use some contact protectant/enhancer like Caig Labs Pro Gold. That would probably give you a good long period of safe running. You will definitely need to clean and enhance the mobo side and I would want to either get a replacement PSU or install a new batch of contacts on those +5 wires - but even those would likely work well (changed my mind - see "Oops" above! - PSU side needs replacing) with a good cleaning and enhancement - you could also tighten the female contacts with a jewellers screwdriver - using a magnifying glass, you will note that the female contacts are split down the middle - there should be almost no gap at the split. If there is a noticeable gap, then they need tightening.
. IAC, I doubt that either the mobo or your PSU is much the worse for the experience.
.bh.
re. the receipt issue: They are wanting proof of ownership as they have limited their warranty to the first owner. I know that the date of mfr. is right on the PSU but most don't allow just that any more. .bh.
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