Why can't I scan specific files or folders?

AVG Performance
1

After going to the option "Scan specific files or folders" there is no possibility to do so.
"Start Scanning" box is blackout. 
Besides, why can't I scan my external hard drive or just a simple pen drive?

2

Victor, Which AVG product are you actually using?.
AVG Guru

3

Victor, Which AVG product are you actually using?.
AVG Guru