A loud pop noise

Sounds like a capacitor blew. Hopefully it was on the motherboard so you should be OK to try again.

Possibly could have been some capacitors popping due to a short somewhere in your system. Does your PSU power on? You can test it out of the system by bridging the green, as well as a neighboring black wire on the 24-pin connector.

You can do a quick check of the PSU. Use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

This checks the PSU under no load conditions, so it is not completely reliable. But if
it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

Then breadboard the system (build it without a case) to test the parts.
http://www.tomshardware.com/forum/262730-31-breadboardi...

You can build it in stages, step by step, testing as you go.

Then before you start putting components in the case, take a look at this thread:
http://www.tomshardware.com/forum/261145-31-read-postin...

The checklist at the beginning of the thread may keep you from making common mistakes that many builders make.