mac mini model a1347 no display signal

Are you certain the monitor is still working properly? Connect it to another computer to find out.

Switch out the monitor cable with another known to be good cable.

Try resetting the NVRAM. The NVRAM is a special memory section on your Mac that stores data that persists even when the Mac is shut off, such as volume settings and screen resolution - it's the information the computer uses to maintain settings after a reboot. You may have to do this several times because sometimes that's what it takes to stick. Press and hold the keys at startup until you hear the Mac chime 3-4 times, then release.

Reset the NVRAM

How to Reset NVRAM / PRAM on your Mac - Apple Support

Reset the SMC

How to Reset the SMC of your Mac - Apple Support

If rebooting your Mac doesn’t fix things, see if the problem still happens in Safe mode (hold the shift key down at startup). It can take much longer to safe boot (10 min) so be patient.

How to use safe mode on your Mac - Apple Support 

Safe mode disables loading third-party drivers, forces the OS to do disk repair, clear certain caches and logs and other miscellaneous housekeeping. It's non-destructive to user data so is safe to do. Very often certain weird software behavior is corrected by simply logging in this way as a troubleshooting method. When you're in safe boot, the machine will not be at its best performance, especially with graphics, but that's expected.

Does the problem persist while in Safe mode?

Exit safe mode by restarting your Mac normally and re-evaluate the issue again.

If the problem is still unresolved, please return here and post a reply and we’ll see what else we can come up with for help.

The A1347 identifier covers all of the Mac mini models between 2010 and 2014.

If you identified the year model and the display, then it would be a lot easier for us to provide a solution or alternate way of providing video out to your display.

Late 2012