Various problems on iMac running 10.5.8

Question

My iMac has been out of Apple Care for about two years now. I have replaced the hard drive about six months ago.  Now the screen sometimes appears to "smear" the graphics or words in an area. Sometimes running the cursor over it clears it up and sometimes only going to a new page does.  It is also freezing up pretty frequently. I have plenty of free disc space.  When it freezes, sometimes the ball is spinning and sometimes I just see the cursor arrow. The cursor or ball will move but will not do anything.  So I can't change pages, tabs, or apps.  It also doesn't work to hold down control-apple-escape.  Nothing happens with that.  I have run disc utility and repaired permissions. Anything else I should try? I can't afford a new computer! Thanks. 

Answer 1

Here are instructions for resetting them:
SMC RESET
• Shut down the computer.
• Unplug the computer's power cord and all peripherals.
• Press and hold the power button for 5 seconds.
• Release the power button.
• Attach the computers power cable.
• Press the power button to turn on the computer.
PRAM RESET
• Shut down the computer.
• Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
• Turn on the computer.
• Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.