iMac getting Super hot + screen Flickering

All I am looking for some advice i have had my imac for around 18 months its a 2.7GHz Intel Core i5 with 4 GB of RAM for the best part it has been fantastic infact i would go as far to say i love this machine.

Unfortunatly over the past few weeks the screen has started to flicker then the screen goes off. when i press the power button on the back it comes back on and everything i was working on and all programs opened is still there.

I have noticed that the top of the mac is becoming very hot (not sure if this is normal and only picked up on it because of the flickering)?

i have also noticed that the left hand side of my display is starting to become darker than the rest of the screen.

does anyone know if this a known fault and more importantly does Apple know about this fault?

Thank you in advance

Aaron