Atmega328 doesn't respond after power loss while uploading program
In my experience, @Jansen's comment is basically correct. The common thing that I've done in the past is accidentally programmed the fuses so that the clock source is for an external crystal, for example. If you do that, and you don't have a crystal (and load capacitors) attached in the right frequency range for the fuse settings, none of the chip's functions will work anymore, including programming. It's very difficult to know exactly what setting you inadvertently changed without the use of a high-voltage parallel programmer at that point. But if you've got a crystal circuit handy, you could try connecting it to the XTAL pins and see if it helps revive the program-ability of the device.