iMac freezing issues

I have been having freezing issues w/ my late Nov 2007 20" iMac 2.4 Ghz lately. And, i would like to know what is causing it. And, perhaps find out if it is an isolated case or something like an epidemic.

These issues would start out w/ apps, like, PSE 4, for example, unable to force quit. The PSE icon in the dock is still lit up, but I can't reopen or do anything with it. I have had this problem before but it has recently been more frequent. Last night, I had to shut down the computer 3 times within a few hours of each other. Not good. Since, these freezes have been occuring more regularly, I know exactly what the computer will do or won't do. For example, if I have an external firewire drive that is docked, I won't be able to eject it. So, the problem creates a kind of like chain reaction. While some apps are unresponsive, some apps remain responsive. So, I can use Safari to browse the internet, for example. But, I can't continue to use my computer normally b/c it is obviously not behaving as it should. I wanna restart it! Or, better yet, go into Activity Monitor and maybe force quit the unresponsive apps that way since hitting right click on the mouse or cntrl-alt-esc doesn't work either. Maybe, I can do it in Activity Monitor, I say to myself. But, inevitably, Activity Monitor will not start and this usually freezes the entire computer, in which case I have to shut it down by pressing the power button.

I wanna throw the computer out the window or do a clean install and not upgrade to leopard. My iMac came w/ a separate Leopard CD that I had to install myself. It originally had Tiger in it. My reason to stick w/ Tiger is that my 5 yr old powerbook w/ OS X 10.4.11 never has these issues.

I have already started backing up my files, in case, the iMac dies. I hope it gets better. I really don't want to have to shutdown the computer 3 times every night b/c of these freezing issues. If it continues, i will probably have no choice but to do a clean install as annoying as that is.

Sorry for such a long post. But, I really wanted to make sure to be as detailed as possible in the hope that it might be diagnosed easier. Any input, solution will be much appreciated. Thanks in advance.

 

thanks guys for your swift replies.

i think i will try creating a different user account as suggested and also verify and repair if necessary. i hope the hard drive is ok, though, as i don't have cash to send it to apple and i don't have apple care. the alternative would be replacing the drive myself, if it is broken, which is a daunting task w/ an imac.