Hello. My iMac has just had new RAM installed and the OS has been upgraded to 10.7.3. Now it freezes randomly. Cursor won't respond to either keyboard or mouse, and clock stops keeping time. No error messages or spinning beach ball, just freeze. I have to press the power button to force it to shut down. Once I start it again, it may freeze again right away, or it may run for several hours before freezing. The freeze can happen when I have just a few things open (such as a single Firefox window with two tabs open, plus a font management program called Suitcase), or when I have these open plus iTunes, TextEdit and Calculator. Often (but not always) I have been playing a downloaded podcast in iTunes, or trying to stream audio or video through Netflix or Live365, when the freeze happens. I've also tried unplugging and re-plugging both the keyboard and mouse from the USB ports, and plugging the keyboard into a different USB port. The RAM install increased the RAM to 6 GB. The OS upgrade took the OS from 10.5.8 to 10.7.3. On the advice of the local authorized Apple service provider who installed the RAM and performed the OS upgrade, I used Software Update to install 10.7.4. This hasn't fixed the problem. This iMac was previously almost completely trouble-free. I think this is a 2008 iMac but not sure how to find that information. I know that the AppleCare has already expired on it. I didn't do the OS upgrade or RAM install myself. So as soon as I can get in touch with the local Apple tech who performed them, he's the one that will actually be responsible for diagnosing and fixing the problem. My only reason for upgrading the OS and installing more RAM is to be able to run Adobe Creative Suite 6 when it's available. I've read through several posts here on the iMac forum, but couldn't find a description of anyone else's problem that matched mine exactly. Thank you all for any insight you can provide.