First:
HB units can be booted into 2 Simulators without a transducer attached.
Point-of-Sale Simulator Mode is the default when you boot and let the boot continue. Any changes made will be discarded when rebooted.
Full-Simulator Mode can be entered by pressing Menu-key on boot-screen and selecting Simulator. Any changes will be retained.
You want to boot into Full-Simulator.
After your HB unit is booted into Full Simulator, then insert the SD-card with your waypoints. You should be prompted to load Yes/No, select Yes.
The MATRIX folder on a SD-card can contain several files.
DATA.HWR file will contain all waypoints and routes. HWR--> Humminbird Waypoints Routes
nn.HT files will contain any HB Tracks. Each Track has its .HT file, 000.ht, 001.ht, ... nnn.ht
Be sure to insert your SD-card AFTER the HB unit is running.
Sometimes on problems it is easier if we know the software levels of you HB unit and HBPC. . .