Do you see either the TX or RX led flash once?
If not, it may be that the computer takes a while to compile the sketch, and so by the time it tries to upload it, the bootloader has already timed. You may need to press upload, wait a few seconds, and then reset the board. Try various pauses from 1 to maybe 15 seconds. Resetting the board multiple times doesn't help, you just need to get the timing right.