First check the wiring is all connected (you might need specific removal tools to get the stereo out of the dash - a penknife might suffice)
If it looks all connected securely, try fitting a new fuse.
Cheers. I assume you need some form of 12V power supply to test the head unit. Although I've just found my multimeter isn't in the toolbox where I thought it was so this could be a non-starter.
Easy was is to check the main fuse, find the fusebox and see if there are any blown fuses. Or looking the manual if it has one, or google to see what number the fuse is, and if the radio fuse is shared with some else such as the cigarette lighter if it has one and see if that works.
First check the wiring is all connected (you might need specific removal tools to get the stereo out of the dash - a penknife might suffice)
If it looks all connected securely, try fitting a new fuse.