I've been doing all sorts with my Uno over the last week, but after making a few small tweaks to my latest sketch this evening, I couldn't get it to upload. I get the following error:
avrdude: verification error, first mismatch at byte 0x0000 0x0c != 0x62 avrdude: verification error; content mismatch
It won't even let me upload the standard 'blink' sketch.
I've disconnected everything from the board, tried a new USB cable in a new port, tried resetting the board immediately before uploading. Always the same error.
When I push the reset button, led 13 flashes then stays on permanently, sometimes flickering a little.
When I upload, the TX and RX lights flash, but after the error it's back to led 13 staying on.
Googling indicates either a fried board or the need to replace the bootloader.
Edit: it's perhaps also worth noting my MacBook has had a kernel panic and shut itself down three times today (an otherwise incredibly rare even) while doing stuff with the Uno.