My iMac keeps shutting down everytime I do a video call on skype

[tzeeyoong]

I'm a first time iMac and skype user. I downloaded skype 2.7 earlier today and managed to do a video call for 30 minutes without any problems. However, after trying to use it again 3 hours later, my iMac keeps shutting down everytime I make a video call. None of my video calls last more than a minute before my computer shuts down. I tried reinstalling skype from scratch again but t didn't work. Even the beta version failed to solve the problem. Please help. I'm new to both iMac and skype. So please guide me step by step. Thank you.

[spinnerlys]

How does it shut down?

Is there a message like this (http://support.apple.com/kb/HT1392)
http://km.support.apple.com/library/APPLE/APPLECARE_ALLGEOS/HT1392/106227_3.jpg

or does it simply just switch off?

[tzeeyoong]

It just switches off. No messages or warning at all. Can you help?

[Mooganic]

Check your GPU temp using istat pro or similar - perhaps the video is causing the GPU to overheat.

A rapid shutdown like yours is sometimes caused by bad RAM or mismatched RAM pairs.

[tzeeyoong]

How do I do that? I'm very new to iMac and have not much clue what I'm doing :confused: