I cant install 16.04.2 on my Pi , i only have access to windows computers to create images.
Stucks on rainbow screen
If you have access to a RPi 3 B, you can use it to update the necessary features of the Ubuntu MATE 16.04.2 RPi image so that you can then transfer it to the RPi 3 B+ to get it to boot through the rainbow square screen. It is then necessary to update the WiFi firmware. I am not convinced that this necessarily gives you a fully working Ubuntu MATE OS although this may be my Linux inexperience talking.
If you don’t have access to a RPi 3 B, then one option would be to download the Astroberry server image by R Kaczorek. This is an Ubuntu MATE 16.04.2 image loaded with lots of software (for astronomy/astrophotography) which works directly on the B+. You could remove some of the software applications if you don’t need them. By the way, it wakes up until first modified as a WiFi Access Point Hot Spot, but you can modify the WiFi settings to gain access to the Internet, or use the Ethernet port.