I have a Dell Inspiron I14-5448-830 (touch screen), with i7 and ATI Radeon Graphics. The native OS is windows 10, and i have dual boot with Linux (i have disabled the secure boot, Linux uses legacy boot, windows uses UEFI.
I have used Ubuntu LTS 18.04.1 about 2 weeks, without any problems. Yesterday, the screen froze, and i have needed to restart by pressing power button. After restart, only what the screen showed is a blank screen with underscore flashing _, and if i boot with SHIFT key pressed (to force GRUB), the screen showed GRUB _.
The CtrlAlt+(F1 or F2 or F7 or F's) or any keyboard key doesn't do anything.
I have tried to format with Ubuntu LTS 18.04.1, or with Linux Mint 19, and the problem persists. It is important to say, the Linux at live USB works perfectly. Before format, i have swept/brushed the hard disk Linux partition on windows with EaseUS Partition Magic.