Checking drive for errors & defragmenting

I've been having trouble opening programs, computer freezing up, and errors stating that I don't have enough resources when I try to open more than one program.  So now I am trying to defragment my C drive to see if that will help but my computer freezes up during the process.  On the first few tries, the defragmenter would start over after 5% stating that the drives content was changing.  When I press ctrl alt delete to see which programs are running, there are about 15 listed that I didn't open.  So I close all of those and go back to defragmenting.  Now it won't get past 56% without freezing and having to shut down.  I get the same when I try to check the drive for errors.  I'm stuck, I have no clue why those programs are running, when I restart my computer all the same programs are listed again.  They are not set up to run at start up.  Any suggestions?