Intel imac 24" seems to overheat top LH corner and goes to sleep

Question

Intel iMac 24" - Since upgrading to Lion, my iMac keeps halting - particularly whilst playing back video - and goes into sleep mode.
The iMac is very hot in the top left hand corner so I assume that there is a thermal safety cut-out that is putting it to sleep ?
Tapping the keyboard a few seconds later staarts it up again but very soon heating issue causes it to go to sleep again.
I've never opended it up so I don't know what componenet is sitting in the top LH corner that is getting very hot - suspect its the graphics card.
anyone else had the same issue and know how it can be resolved ?
tia,
Max

Answer 1

Your machine is working kind of hard, the first thing I'd try is doing both a SMC and PRAM resets, in fact doing 2 of each wouldn't hurt.
With only 493MB of free RAM you should upgrade. One thing you can check when you do this is to see if there is any dust that has accumulated on the intake port, this could be obstruction air flow. Do NOT blow are in but you can vacuum it out. I would recommend using www.macsales.com (OWC) and Crucial as vendors. I prefer OWC because they specialize in Macs so you know what they sell works, have terrific customer service and competitive pricing.  BTW OWC has how-to videos that show how to install RAM.
SMC RESET
Shut down the computer.
Unplug the computer's power cord and all peripherals.
Press and hold the power button for 5 seconds.
Release the power button.
Attach the computers power cable.
Press the power button to turn on the computer.
PRAM RESET
Shut down the computer.
Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
Turn on the computer.
Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.