both screens you are describing represent the computer failing to identify a startup volume.
wihout a second mac or an install disk, you are out of luck at the moment. should you find somone else with a Mac, you can start up your computer in target disk mode (holding "T" at startup), connnect it via firewire to another Mac, and try to repair your harddrive via disk utility on the second Mac, or in the least, get your data off.