Are you getting any receive "bars" on the top right side of the screen when it's scanning the p25 system? Also, if you press the "hold/resume" button while it's scanning the trunked p25 system, it should stop on the site it's receiving and show the site Id and frequency.
One other potential problem, on my state p25 system, Freescan sets the system type to "Mot Type II/P25", it should be "P25 Standard (digital xt)". Now, I don't know for sure if that will cause it to not receive anything, but I know p25 standard works on my system.
These are just some basic starting points to make sure the basic setup and location of the scanner is ok.
Jeff.