Hi fly babe,
When you click the
Start button, the next pane you see is entitled
Preparing System Scan.
The last option in the list say
Activate in-depth scan (recommended). Make sure that the little radio button is green (it also has a tick in it). If it's red (with a cross) then just click it, and it will turn green. I was going to post a screen shot, but haven't worked that one out yet.
Cheers
Liam