Help please!

Whenever I run a system scan, it works for the most part. But then, when I'm just about done, it stops scanning. It shows up on the screen as if it's still working, but the number of scanned files just stops growing. I've come back to it numerous times to find that it is still on the same number. So, whenever I stop the scan, a message comes up asking me if I want to do this. I say yes, and it keeps scanning! I try closing the window, same thing happens. Eventually, I end up having to end the process.

Now, this morning, the status changed. It said that some things "need attention." I click on "fix now," and it begins trying to install updates. This is where I'm really stuck: every time I try to do this, it successfully downloads the updates, but fails to install them.