White screen of death on iMac, will not boot in safe mode or from disk.

21" iMac, intel-based, bought early 2009.

No problems until now. Thought fan was running hard, shut down the computer thinking maybe it needed to rest. When I attempted to turn it back on half hour later, I only got the white screen with a question mark folder icon. Tried cmd-option-p-r, tried smc reset, tried to boot in safe mode and no response. Tried to boot from disk and got apple icon but the disk ejected.

Would love some other ideas to try, or info about what could be wrong and what it might cost to fix. Thanks so much!