hmmm, its a tricky one but lets break it down.
You say you can hear what you are playing. That does not prove communication with the PC, cause the signal from the guitar to the headphones is routed through fast track and not the PC....
However, controlling the main volume level through control panel shows communication.
So it seems to me,, USB ports, USB drivers, Fast track communication board and Fast Track Ports are all working fine. 
What's Left:
Pro Tools issue. There might just be some corrupted files. So try Re-Installing it tonight. Or try it on another computer- could also be an OS corruption inflicted by a virus or spy-ware. If the problem still persists I think you should take it in for testing.
At the end of the day it could actually be anything, working with PC's my whole life i have noticed there is something called " The Ghost in the Machine " where issues just does not make sense @ all...
NOTE: Pro Tools also, is sooo jelous, hahaha. Last night I ran both Pro Tools and FL-Studio together and I got like 6 error messages from SE, froze up- and refused to open.. It's like it just told me--
I WORK ALONE !!!!