Just installed 18.04 on a Lenovo Carbon X1. It worked fine for a few days, but now when I boot and select Ubuntu 18.04 on the GRUB selection screen, the screen goes purple, then black. There's no Ubuntu (....) splash screen, but the desktop shows up for a split second before going to a black screen with a mouse pointer that I can move around.
When I go into recovery mode -> resume, everything seems to work fine but the resolution is different (onscreen text is smaller).
I can get into tty2 but running startx doesn't work.
Here's my video card info:
00:02.0 VGA compatible controller: Intel Corporation UHD Graphics 620 (rev 07) (prog-if 00 [VGA controller]) Subsystem: Lenovo UHD Graphics 620 Flags: bus master, fast devsel, latency 0, IRQ 255 Memory at 2ffa000000 (64-bit, non-prefetchable) [size=16M] Memory at 2fa0000000 (64-bit, prefetchable) [size=256M] I/O ports at e000 [disabled] [size=64] [virtual] Expansion ROM at 000c0000 [disabled] [size=128K] Capabilities:  Vendor Specific Information: Len=0c <?> Capabilities:  Express Root Complex Integrated Endpoint, MSI 00 Capabilities: [ac] MSI: Enable- Count=1/1 Maskable- 64bit- Capabilities: [d0] Power Management version 2 Capabilities:  Process Address Space ID (PASID) Capabilities:  Address Translation Service (ATS) Capabilities:  Page Request Interface (PRI) Kernel modules: i915