Capacitor likely blew. Examine each one on the motherboard.
either that or a voltage regulator.. Prolly a lot harder to spot if so.
IF the sound came from your computer, it's either power supply or motherboard. Period.
But, are you sure it's not from the monitor? Have a spare one to just check and see?
If monitor checks out, then replace the power supply, if not that then it's the motherboard.
Might be both too, if the PSU blew the wrong thing.
We've had motherboards where a couple inches square turns into a charred mass due a PSU going out in a server. Crazy shit can happen.
Just because the PSU is powering up your hard drives/fans does NOT mean it's supplying proper voltage to the cpu/other components on the motherboard.
Also, if you are savvy enough you can likely tell if it's the monitor simply by listening/watching the hard drive lights. If they appear to blinky blink like the box usually does when it boots up, start w/ the monitor as it's likely your box is fine.
Good luck.
-Phil