2000 Toyota Celica No oil! :-(

My poor car started making a 'tick tick' type noise which gets faster and louder as I accelerate through the gears. I cant hear anything when she is at a stand still and when I rev it.

I checked the oil and found it was 99% empty, and I never had any worning light on my dash! :-(
I immediately topped her up with oil and then drove home from work, the noise is still there!

What damage have a caused and is it going to be fix-able or costly? My poor baby! :-(

Laura