I have a PC with Via Chrome9 onboard graphics, I used a bootable USB with Ubuntu mate and the resolution was fine but after installing it the resolution remained at 640 × I don't remember but I can't change it I need help
Main Menu -> System -> Preferences -> Displays
That should at least get you 800x600.
If it doesn't offer you anything other than 640x480, you'll need a driver for your card: should be xserver-xorg-video-openchrome, but IDK for sure.
sudo apt install xserver-xorg-video-openchrome
if so.
I installed it and now before login the screen stay black "no signal"
Well, that's not good... 
Did you do the first thing first, and if so did it offer you 800x600 or any other resolution better than 640x480?
Boot into recovery mode and sudo apt remove xserver-xorg-video-openchrome.
It "should have worked", but it's a rare driver, so you might have more luck seeing if anyone on askubuntu.com with the same card knows how to get it working.