MacBook Air won't start up

Case No. 243441309
(800)MY APPLE
Troubleshooting steps:

Preceding event:  Startup disk was full. 
I didn't know how to empty trash.

1. Turn off computer
2. Turn Power Button
3. Press simultaneously Command Option "P" "R"
4. Hold down until you hear 2nd chime

OS is Snow Leopard, 128 Gig HD

Troubleshooting Step B

1. Insert USB reinstall driver USB drive
2. Turn On Power
3. Press C for language, hold down

Troubleshooting Step C

1. Shut down
2. Shift key after you hear sound
3. I was able to go to desktop. 
4. Trash can at the lower right hand corner.  Click on it, empty trash.

Moral lesson:  Something as simple as emptying the trash can create havoc if you react rather than solve.