Fingerprint reader problems with Latitude E6420xfr

Fingerprint reader problems with Latitude E6420xfr

I bought a  used dell latitude E6420 XFR with fingerprint sensor(I can see it on the right side of the pad).
The OS was Ubuntu so I reinstalled a windows7. But after installing all drivers et al., neither the DDA software nor the windows control panel could find the fingerprint sensor.
I contacted service staff and she says that my laptop does not include such a sensor according to the service tag(but I see it), so it's just a "dummy".

The problem is, I checked the manual downloaded from dell.com, and find that there are some version of e6420xfr without the sensor and there is not a little "gap" on the pad, and mine have such a "gap".

So, what am I supposed to do to get it work, or it just cannot work?

I figured out some ways but I don't know if they will work, or there's something I still don't know:

1.install "some" drivers - I installed all from dell's support program, but nvidia's video card driver didn't appear and I installed myself. I don't know if there's a driver that I can install, at least I cannot find it on dell.com.

2.disassemble my conputer and check if that sensor is a "dummy" or if it's connected well. This could take some time...