I bought a cintiq pro, but my computer doesn't have a display

You mean like the cintiq needs a vga port? You can get a hdmi to vga adapter for like 3 bucks, so I would try that.

>>3065219
I'm pretty new to this, but to connect the cintiq, you need either a usb-c without adapter, or a minidisplayport with the adapter on your computer. My computer only has an hdmi port, but apparently people have tried to connect their cintiqs with an hdmi-mini display but the screen wouldn't show up. There are ways to connect using minidisplay and display but my computer doesn't have that.

>>3065226
Ah I see, I don't know much about the cintiq so I was pretty much guessing. If your computer doesn't have the options to use what you need to display it, then I would return it. You can try and see if any of the other display tablets will work with your pc.

https://www.amazon.com/MSI-GT-1030-2G-LP/dp/B071L4VKF6/ Here's a cheap nVidia GT 1030 that has a DisplayPort. May not be great for gaming, but as a bare minimum solution for your tablet it should work.
You'll probably also need a Wacom Link, but you can use this. I'm not sure if a USB-C add in card would work if your CPU didn't have an integrated gpu.

>>3065203
>>3065226
HDMI/displayport adapters exist, don't they?

Check monoprice