原因看看下边这个参数的作用就明白了
nomodeset
The newest kernels have moved the video mode setting into the kernel. So all the programming of the hardware specific clock rates and registers on the video card happen in the kernel rather than in the X driver when the X server starts.. This makes it possible to have high resolution nice looking splash (boot) screens and flicker free transitions from boot splash to login screen. Unfortunately, on some cards this doesnt work properly and you end up with a black screen. Adding the nomodeset parameter instructs the kernel to not load video drivers and use BIOS modes instead until X is loaded.翻译
最新的内核已经把视频模式设置嵌入内核中，所以所有显卡硬件程序的指定时钟和寄存器当图形服务器启动时在内核进行而不是图形设备运行，这使得我们在启动时可以看到不闪的和高分辨率的好看的启动界面，但是，在某些视频卡它不能正常工作而现实黑屏，增加nomodeset参数则告诉内核不要加载显卡而用BIOS模式直到图形界面运行
先别拔U盘，用“Try Ubuntu without any changes” 进去修改硬盘里的/boot/grub/grub.cfg，把quiet splash后边都加上nomodeset，再拔U盘重启
