I have a GTX 550 Ti and I tried overclocking it today, I added 50 to the GPU clock offset and the Mem clock offset, with the voltage at 1067.

I ran Furmark while I did things on my phone, and instead of crashing (like it did before with my Mem clock higher) it shut off my PC; I periodically checked the temp of my GPU every 30 seconds and it never went above 73.

I figured it was the PSU, but there's a glowing red Power and Reset button on the inside of my PC, which I don't think would be glowing if the PSU was busted.

So what else could have happened? Is temperature of my GPU not the only thing that could've fried it? Or does Overclocking my GPU do things to my other components that I wasn't even aware of checking?

EDIT: Corsair Carbide 300R ATX Mid Tower PC Computer Case

OCZ Deneva2 256GB SATAIII SSD

AMD Phenom II X4 940/840T 108W CPU Unlocked

8GB Kingston DDR3 RAM

Seagate Barracuda 3TB Hard Drive

ASUS M4A79T Deluxe AM3 Motherboard with 4x PCIe x16 bus lanes (Latest BIOS)

Nvidia GeForce GTX 550 Ti

Cooler Master Vertical CPU Cooler

1 200mm adjustable fan

2 120mm fans

Apevia 500 watt power supply

EDIT: It was Furmark that caused it, and it was the PSU that failed. Everything's good.