What blew?
 

When changing a network card in one of our computers we ended blowing it up. Turns out it was on but in standby or something. So when the other network card was put in it popped, smelled horrible, and now wont power on.
So my question is What can i fix or is everything ruined? I took the ram out it works in the other computers. I hope the hard drive is good, and the graphics card etc. . . .

Any help is greatly appreciated.

Modern ATX motherboards still have 3.3 Volts running through them even when "off." You have to remove power from the power supply before tinkering. You probably fried either your motherboard or your power supply. Be careful if you intend to work on the power supply. Getting zapped sucks.

it might just be the power supply. I'd look for blown capacitors or transistors or anything like that on the motherboard as well. I'd place my money on the PSU though.

Definetly the PSU, have another you can quickly swap out and try. That would be the easiest and quickest test.

You need a new power supply...
But other components may have been damaged from that. Good luck.

You have to unplug the powersupply when changing components?

Now that is not what I've been taught. I've been told that it's safer to leave it plugged in (and therefore grounded) in order to dissapate any static electricity you may have on your hand or clothes.

Granted, pulling a component out while a system is powered (or in standby...) is probably a reeeeally bad idea.

Every ATX power supply I have ever seen has a switch on the back to cut power, so I never unplug anything. I do make sure I hit the switch before messing with anything inside the computer.

The smell most likely came from the PSU, however it's also very likely that the burning smell came from something on or attached to the motherboard. Most likely culprits would be the NIC and the motherboard.