Problems with Inspiron1525 freezing and can't defrag

My computer will freeze, kind of. I can still move the mouse around but cannot get the hand to click on anything. I am running Vista and my task manager has stopped coming up for me. I researched that and have found a lot of people are saying that. So I have to shut down with the power button. Sometimes when I restart it will say they recommend that I have a disk checked for it's integrity or continuity, I forget. So I went to defrag to see if that would help at all and it ran overnight and was still running so I cancelled it. I tried again and it ran all day and I cancelled it. I must admit that I have not run it in a long time as I wrongly assumed my virus scanner was running it and just realized it does not. Can anyone help me with any or all of these problems? How long should I let the defrag run, how long is too long. With Vista you can't see the progress you just see that the circle is still moving which it has been each time I cancelled it. I am trying to stop what I am afraid is a major problem! Oh, one other thing, the asking me about checking a disk didn't start until after I had bought an external hard drive to move all of my pictures onto. I don't have it hooked up the the laptop anymore, it is on my desktop. Could that have anything to do with the message??? HELP!!!!