Mavericks Crashing my iMac 2012

I also had a crash today, computer just hang while browing on safaring, had to hold the power button to reboot, machine is the new 2012 27" imac, hope apple does an update as mountain lion was so sweet on my machine & i miss it now 😟

You could try a Safari reset and to clear the cookies in Safari preferences. What Safari extensions do you have?

A Force Quit may have been simpler than powering off. (Opt+Cmd+Esc)

Ok wil trying doing a reset & clear the cookies, i have no extra extensions just what comes with it.

There was no response to anything, even the cursor disappeared, well will try force quit if it ever happens again.

I'm not sure what "comes with it" entails. Adblock has a "go faster" feature which causes blank white pages and needs disabling.

well my safari made my computer hang after i clicked on "Top Sites" feature, i just upgraded maverick from mountain lion so all my earlier safari settings & top sites got transfered to the new safari of maverick, so in the Top Sites fature the websites snaps looked abit weird & zoomed in comapre to what they look now after doing a Reset as you said, lets hope the reset solved the problem.

Reset the iMac's SMC. Read all the steps. You may not be able to perform the ones under Before Resetting the SMC so just skip to the next section.

Before Resetting the SMC

Try each of the following steps in this order before you reset the SMC. Test the issue after completing each troubleshooting step to determine if the issue still occurs.

1. Press Command + Option + Escape to force quit any application that is not responding.
2. Put your Mac to sleep by choosing the Apple () menu from the upper-left menu bar and then choosing Sleep. Wake the computer after it has gone to sleep.
3. Restart your Mac by choosing the Apple () menu from the upper-left menu bar and then choosing Restart.
4. Shut down your Mac by choosing the Apple () menu from the upper-left menu bar and then choosing Shut Down.

Resetting the SMC for Mac Pro, Intel-based iMac, Intel-based Mac mini, or Intel-based Xserve

1. Shut down the computer.
2. Unplug the computer's power cord.
3. Wait fifteen seconds.
4. Attach the computer's power cord.
5. Wait five seconds, then press the power button to turn on the computer.

Attempt to start the iMac in Safe Mode again. Reply with your results even if there is no change.

Am having exactly the same problems - only get to stay on for 3/4 mins then shuts down - will not let me transfer any files to a hard disk - has corrupted my back up drive . When installing mavericks it got to the final stage of completing installation 7 mins then 6 mins then it crashed - restarts and tells you there was an error shutting down. - even crashes just sitting on login in window for 3 mins. Have quickly tried to reinstall maverick twice and it goes through the stages if I am quick enough but exactly the same things happen - if it was installed properly it shouldn't let me do this - on computer shows system as 10.9

Also happens in safe mode

Two potential problems remain: a corrupted OS X installer, or a hardware failure:

Unplug all external hardware, which should be everything connected to the iMac unless you are using a USB keyboard.

Run Apple Hardware Test by holding⌘ option d (three fingers) while you start your iMac. Run the extended tests. It may take 45 minutes or so. It is very likely to report "No trouble found" but if it doesn't, write down the error and report it.

Then, shut down the Mac and boot OS X Recovery by holding ⌘ and r (two fingers) while you start your iMac. At the Mac OS X Utilities screen, select Reinstall OS X. Once it completes an hour or two later, test your Mac again for operation. Start with Safe Mode, and if it does not crash perform a normal boot.

I have no idea if this will help. I've tried others suggestions, like unplugging the keyboard and replugging it; didn't work. I tried restarting; didn't work. I tried rebooting in safe and repairing disk permissions; didn't work. I tried everything. Then I thought since sending over 20 crash reports out to apple didn't really seem to be getting any results, (I'm sure they are busy fixing other things) I will continue to tinker with my system, which hasn't been stable for a full day, until the last two days, where I haven't had one crash yet. Here's what I did that seems to have worked, although I cannot guarantee any results for anyone else:

Go into system preferences, security&privacy and turn OFF what Apple suggested to turn on, that is 'Require Password XX hour aftersleep or screen saver begins. Mine is now unchecked. The next box is also unchecked (show a message when the screen is locked) and the next, 'Disable automatic login' IS checked.

The other thing I changed was Setting the diplay, under 'Energy Saver' in system preferences, to Computer Sleep: NEVER and Display sleep: NEVER. Wake for network access is also checked under the energy saver system preferences.

That's all I changed and my system seems to be stable now. I haven't had a restart in 2 days, and I had over 20 previous to that, since upgrading to Mavericks.

Please let me know if this helped anyone or if this too, is just a flukey 'worked for me only' suggestion.

I don't suggest doing this on a laptop that's not secure, though, as you run the risk of keychained passwords being accessed. I live in a secure building and am on an iMac (2009) so thought it would be fine to disable screen security settings as there is limited access to my building. Good luck, hopefully Apple will come out with an update to prevent these random crashes. It's incredibly annoying and negligent, that they didn't test all models of computers that Mavericks would be approved for and installed on. Everything has its price, I guess, and this software update certainly wasn't 'free' as it has cost me tonnes of time and lost revenue from work.