what does this error mean (avrdude: stk500_getsync(): not in sync: resp=0x00)

Hey guys,

Been using Getting Started with Arduino. The last sketch I uploaded was Dimming the led with a variable resistance UV sensor. In place of the UV sensor I used a 300 ohm to 1.2kohm pot.
I was using linux for my sketches and now the DIM sketch isnt even in my sketchbook anymore so i cant show you.

I uploaded the sketch and the led came on connected to p9 but didnt dim. Went to bed and went to use it the next afternoon and its no longer recognised by Linux or windows on my desktop or laptop.

Please help me figure this out. Thanks heaps!!