Urgent help if possible

ive just bought a second hand imac.

when i turn it on i can hear the fans start up but nothing shows on the screen.

i can connect an external screen and that works but the main imac screen isnt working, ia there anything i can try?

 

ive decided to test out the applecare first.

i got the mac for a bargain price and it still has 2 years applecare left so thought id take it in for a repair and decide after that.

dropped it off on saturday afternoon and was told it will be about 5 days until its back.

he said it sounds like a graphics card problem so will wait and see.