IMac 2011, screen freezes and fans start spinning

Question

Hello,
I have this really wierd problem with my iMac i5 2011 edition since a month or so...
A lot of times when I am downloading or watching a movie or playing games under OSX on my iMac my screen slowly freezes, it always starts with my finder and then te rest goes, I get the marble of death and shortly after that the fans start spinning like crazy, they start slow but after a minute or so they make a lot of nice. Take in mind then I am unable to use my iMac in anyway, the mouse moves but it doesn't respond to clicks and also my keyboard doesn't respond, I keep getting the marble of death still.
The wierd thing is that sometimes it doesn't do this for 2/3 days and sometimes it does it like 3/4 in an hour (have to restart manually). Also, this is very interesting, I have a version of Windows 7 installed on my iMac wich I use mainly for gaming and under windows it NEVER freezes in any kind, even when I game like 5/6 hours long straight.
Therefor I thought it must be a software problem so I did a complete system reboot 2 days ago but that didn't help, already froze 3 times since...
Can anyone help me? I still have 2 months of applecare but I have a LAN party soon so I am not to anxious to go 3 weeks without my iMac, maybe there is a simple solution that I am missing...

Answer 1

Some things you can try:
1. Try a new user account, create one in System Preferences -> Users and Groups, test to see if the issue still persists in this new user account, this will give us a lot of information. (if the problem is the same or it vanishes, let us know)
2. Make sure all your software is up-to-date, Apple Logo -> Software update.
3. Unplug all 3rd party devices, just keep in the necessary, Power, Keyboard + Mouse, no ethernet or external hard drives etc.
4. Reset the PRAM http://support.apple.com/kb/PH4405
5. Reset the SMC http://support.apple.com/kb/HT3964
6. Boot to the recovery partition (CMD + R on startup until you see a spinning cog with an apple logo, then let go) -> Choose english as the main language -> Choose Disk Utility -> Select your hard drive from the left pane of Disk Utility (NOT Macintosh HD, the one that will look similar to: 1TB ST3200WAJS) -> Select the 'First Aid' tab -> Bottom right of the window it will say 'S.M.A.R.T Status: ________' ... What does it say after smart status?
7. While still inside the Recovery Partition, select Macintosh HD -> First Aid (tab) -> Verify Disk -> Repair Disk (unless it says the volume Macintosh HD appears to be OK) -> Verify Disk Permissions -> Repair Disk Permissions (if there are differing permissions on the disk)
Let us know if the issue still persists, but make sure you do all of those steps correctly and post back as much information as possible (PRAM takes two chimes at startup, unplug the power cable for 15 seconds, plug it back in, wait 5 seconds, turn on... make sure you follow all articles)
Good Luck!
MiiCK