My desktop doesn't have an image signal, what do I do?
Which connectors should you use?
A desktop with a video card has connections on both the motherboard and the video card. If a PC doesn't have a video card, it uses the connectors on the motherboard to transmit a signal. If it does have a separate video card, these ports don't work and you need to use the ones on the video card. Otherwise, you won't get an image. Check if you're using the ports on the motherboard and use the connectors on the video card if you aren't already using them.
Other solutions for the problem
If you still don't get an image after you properly connected to the right ports, check if the cables aren't loose. If this is also okay, you still have the option to update the drivers. Old drivers can give complications for image rendering. You can do this via 'Device manager' in Windows. Doesn't this work either? There's probably a hardware defect and it's wise to connect a new monitor to the desktop.