Question iMac Mid-2011 crashes, freezes or reboots during startup

[Jeremy_95]

I've had this iMac for nearly 8 years and it was working absolutely perfectly until a few weeks ago. Over the years I had added new thermal paste, upgraded to an SSD and increased the RAM to 14GB. One day after not using it for a week however, the loading bar got to about 2/3 of the way and then the screen glitched out and it rebooted. As the title says, sometimes it just freezes or even reboots with no warning. Initially I thought this was a corrupt OS but the same happens even when booting from an external drive. I once managed to get to the login screen but it rebooted a few seconds after. These are the problems I can think of:

1. Thermals - something is overheating?
2. Bad RAM, GPU or CPU?
3. Dead CMOS battery?

Any other suggestions or advice would be much appreciated!

 

[Jeremy_95]

I've had this iMac for nearly 8 years and it was working absolutely perfectly until a few weeks ago. Over the years I had added new thermal paste, upgraded to an SSD and increased the RAM to 14GB. One day after not using it for a week however, the loading bar got to about 2/3 of the way and then the screen glitched out and it rebooted. As the title says, sometimes it just freezes or even reboots with no warning. Initially I thought this was a corrupt OS but the same happens even when booting from an external drive. I once managed to get to the login screen but it rebooted a few seconds after. These are the problems I can think of:

1. Thermals - something is overheating?
2. Bad RAM, GPU or CPU?
3. Dead CMOS battery?

Any other suggestions or advice would be much appreciated!

Ok, slight update - I saw a post that suggested removing the AMD.kext files from the Extensions folder which I did (by moving them into documents) and now I can get it to at least boot using what I believe to be integrated graphics? The experience is not pleasant and there is lots of lag but I think this could either be due to the outdated cpu or the .kext files not being present. I ran out of time to test which file was causing the boot issue however I slowly started adding the .kext files back into the Extensions folder and so far it still works. Benchmarks such as Geekbench can see both integrated and dedicated graphics but can't actually run the compute benchmark (guessing a .kext file needs to be added)?