Look at how much disk space is used, and how full your hard disk is. Go to Finder's File menu -> New Finder Window. Make sure View menu has "hide status bar", if not, click on "Show Status Bar". At the bottom it will tell you how much space is available. Then Go menu -> Compute or My Computer. Select your hard drive icon. Select Get Info from the File menu. That will tell you how much space is used. With those figures we can tell if the hard drive is too full or not.
Please do "About ths Mac" and post what it says for "processor" and Mac OSX version. This forum, in spite of Apple's non-intuituve lableing, is for pre-2006 iMacs which are much different from the newer ones. That can affect troubleshooting issues and recommendation. It does not, however, affect a brody's suggestion which can apply to Macs of any vintage.
Model Name: iMac
Model Identifier: iMac11,2
Processor Name: Intel Core i3
Processor Speed: 3.06 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache (per core): 256 KB
L3 Cache: 4 MB
Memory: 4 GB
Processor Interconnect Speed: 5.86 GT/s
Boot ROM Version: IM112.0057.B00
SMC Version (system): 1.64f5
Is this the info? Help!
You have an Intel iMac. No iMac has been PowerPC (PPC) since early 2006. I've asked a moderator move this thread, and in the meantime I'll attempt to answer your question:
Your machine is from July 2010 to May 2011.
You have exact same model and firmware that I have.
These machines shipped new with 500 GB hard drives, though some were custom ordered with 1 TB hard drives. Double click the hard drive icon (Macintosh HD) in the upper right and make sure the window shows its entirety on the screen at the same time. If you are having trouble with these simple instructions, go to the Apple logo in the upper left corner and select About This Mac, and tell us your operating system. We can then give you specific directions as to what to view or select by operating system.