imac 20 inch 2ghz intel core duo white not booting

[showcow45]

hey my friend is having a problem with his imac when he turns it on he gets a grey screen and stops there. there is also a grinding noise near the back maybe the hd or disc drive? it grinds 10 times then stops then continues for a couple minutes and then he gets a question mark on the screen. can anyone help explain this problem??

[an4rew]

Try resetting the PRAM by holding PR + Control + Command on startup.

But i think the Hard drive is gone... maybe boot from an external drive to test.