First time with new computer

Hello,

I have bought a computer fully built on the internet from LDLC and received it today, so happy i immediatly put him in place, linked with electricity, an old screen and everything, then booted him, then to my surprise, while i expected at least something, the screen stayed black.

the screen works fine and everything is linked, the computer turns on, i did think of turning on the computer with the button behind it.

when i push the boot button, it does start to ventilate and all, get his lights on but the screen stays black.

i have tried using the video cable on my laptop while it was on but it only reduced my laptop screen size for as long as it was linked.

As for the screen, it does stay black but it still shows some stuff like the pic of the analog.

so...i'm not sure, i thought it may be the cable but then why would have my laptop screen decrease when i link my computer with my laptop with the said cable ?

i'm quite lost, i'm sorry to ask for help but i did most of what i could think of.

my computer is a LDLC PC10 Hazmax
Processeur Dual-Core Intel Core i3-4160 (3.6 GHz)
Carte mère MSI H81M-P33
RAM DDR3 8 Go 1600 MHz
Carte graphique NVIDIA GeForce GTX 950 2Go
Disque dur Seagate Barracuda 7200.14 SATA 6Gb/s 1 To
Boîtier Mini Tour Zalman ZM-T4 Plus
Alimentation 500W
Adaptateur interne USB 3.0 mâle / USB 2.0 femelle
Graveur DVD
Microsoft Windows 10 Famille 64 bits

as for the screen it is a SyncMaster SA350