My iMac stalls after about 15 minutes of use

Make sure there's enough available disk space.

Click the Apple  top left in your screen. From the drop down menu click About This Mac > More Info > Storage

Make sure there's at least 15% free disk space. OS X Tips Where did my Disk Space go?

kimberleighfromdublin wrote:

Can you help me fix this problem? My iMac stalls or becomes exceptionally unresponsive after about 15 minutes of use. Every day. Without exception I have to shut it down... leave it down for a few hours and then get in another 15 minutes or so of use.

If you really are on snow leopard -- if you are using the power button you may be putting it to sleep instead of shutting down -- make sure you hold the power button down until you hear it shutdown. In snow leopard under power saver preferences you can change the power button back to shut-off from sleep - don't really know when Apple added that change - as if my Pro was stuck where I had to shut down with power button - I also shut off power to the outlet it was connected to and left the room -- only realized something changed when I wanted to power up immediately and discovered system was sleeping instead of shutting down😠

If you have Safari active and internet connection - it will start updating top sites --

Had the issue with Safari past year and had it had a big chunk of top sites I had to edit out - I now use Opera for web browser.

Hello again, Kimberleigh,

Are you running any kind of cleaning or anti-virus software on your iMac? That is the type behavior one sees with MacKeeper and CleanMyMac. A handy diagnostic tool is the program etrecheck, a free download from http://www.etresoft.com/etrecheck

If you download and run that, then post the output it will be a lot easier to see what is causing the iMac to hang up, if there is a hardware or software issue.

Ralph