I've tried disconnecting the USB hub in case it was keyboard or mouse; it isn't that.
I get the line:
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(179,2)
By the way I have started it several times successfully and noticed that the red light comes on when the USB from the powered hub is connected. The raspi doesn't boot until the mini USB power is plugged in.
Could it be the SDHC card? [It's a Sandisk 8Gb on the approved list}