my power macg3(b&w) only shows this grey background and a blinking grey folder with a '?' in the centre.i tried rerunning the Os (8) but nothing happened.i know a lot about pc's bt this mac cracked me! could it be you with the answer'?' please,my tongue is about to touch the ground,i need help!

The cause of this is that your mac isn't finding a bootable partition with a "System Folder". This may be caused by a corrupt hard drive or missing files. The easiest way to check is to boot from an OS install CD and check the hard drive.