Which Ver of the Maintenance console are you using?
The KX-TDA100D is only supported by versions 7.0, 7.1, 7.2, 7.3 & 7.4 of the Maintenance console of which only versions 7.2,7.3 & 7.4 have Windows7 USB drivers.
Get a latter version of the maintenance console
or get Win7 USB driver from...