Use full Laptop from externel monitor with WD15

Hi,

I use my Precision 3520 with WD15, when i push to type-c cable, the laptop start automaticaly, but i don't see DELL logo or use external keyboard to enter BIOS for example, but the external monitor starts when Windows 10 is starting.

Why i have this issue?

I thinked that i can use my laptop from the start.

Thanks for your help and advis.