screen went grey with Apple Logo

I have just brought a 2nd hand iMac G5 20", this was fully cleaned off and very basic. From advice from a authorised Mac dealer in london i brought a Western Digital 1TB Hard Drive and changed the Western Digital 160GB which was inside. This was changed exactly as it should be and the G5 was closed.

On powering up the machine, the hard drive was then partitioned and formatted, then Mac OS X Leopard Version 10.5 was installed which continued for about 1 Hour following all prompts.

Once finished a re-boot message appeared and this was then carried out.

Upon re-boot the screen went grey with Apple Logo and a pin circle spinning below, this continued for about 2 hours no change.

The dvd disc would not come out nor any functions work, not even power button. The only way to switch machine off is from mains.

I then left fully unplugged for a day and then went back the next day and switched on the power as normal and turned on machine. It has continued to stay on showing the grey screen apple logo with pin circle and this again has not changed for about 8hrs.

Beginning to get a little frustrated and do not know what to do, i am unble to get back into the machines menus etc to delete hard drive and start again.

Please any tech advice would be very much appreciated, this is my 1st Mac and not having much luck

Regards
Dan

Boot from the System Disc/DVD and reinstall the system again. I'd run disc utility off the DVD just to check the drive as well.

Thanks for reply

I have tried that, the computer seems frozen, inserted the disc and nothing it just stays on the grey screen with Apple logo and the Pin circle, also the fans are louder than normal??

You have to restart the machine and hold down the C key...