Debian 9 DM won't load after dist-upgrade

I used to have Debian 8, and today I decided to upgrade to Debian 9. I did so by running: sed 's/jessie/stretch/g' /etc/apt/sources.list sudo apt-get update && sudo apt-get upgrade sudo apt-get dist-upgrade I noticed quite a few weird stuff going on after this. First, the GRUB bootloader is in a way, broken. If I reboot the system, the arrow keys simply don't work (however, if I use the arrow keys, the countdown stops), but the arrow keys do work if I shut down the system and turn it on again. Also, the system fails to boot to the GUI login now, and instead boots to the tty. Here's what shows up during boot, before loading the tty: I tried running startx manually, but that didn't work and gave an error 1, stating, Failed to load module fglrx (Module does not exist 0) I ran sudo apt-get install fglrx but it said there's no installation candidate. How can I fix this? EDIT: Some additional output from some commands I ran. systemctl status lightdm.service gave: lightdm.service - Light Display Manager Loaded: loaded (/lib/systemd/system/lightdm.service; enabled; vendor preset: enabled) Active: failed (Result: exit-code) since Thu 2017-07-06 19:17:26 IST; 2min 18s ago Docs: man:lightdm(1) Process: 864 ExecStart=/usr/sbin/lightdm (code=exited, status=1/FAILURE) Process: 860 ExecStartPre=/bin/sh -c [ "$(cat /etc/X11/default-display-manager 2>/dev/null)" = "/usr/sbin/lightdm" ] (code=exited, status=0/SUCCESS) Main PID: 864 (code=exited, status=1/FAILURE) Here's the output of sudo startx: X.Org X Server 1.19.2 Release Date: 2017-03-02 X Protocol Version 11, Revision 0 Build Operating System: Linux 3.16.0-4-amd64 x86_64 Debian Current Operating System: Linux rahul-pc 4.9.0-3-amd64 #1 SMP Debian 4.9.30-2+deb9u2 (2017-06-26) x86_64 Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.9.0-3-amd64 root=UUID=4fb31b35-931b-4790-8dff-f0b97dd35154 ro quiet Build Date: 03 March 2017 03:14:41PM xorg-server 2:1.19.2-1 (https://www.debian.org/support) Current version of pixman: 0.34.0 Before reporting problems, check http://wiki.x.org to make sure that you have the latest version. Markers: (--) probed, (**) from config file, (==) default setting, (++) from command line, (!!) notice, (II) informational, (WW) warning, (EE) error, (NI) not implemented, (??) unknown. (==) Log file: "/var/log/Xorg.0.log", Time: Thu Jul 6 19:13:40 2017 (==) Using config directory: "/etc/X11/xorg.conf.d" (==) Using system config directory "/usr/share/X11/xorg.conf.d" (EE) Fatal server error: (EE) no screens found(EE) (EE) Please consult the The X.Org Foundation support at http://wiki.x.org for help. (EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information. (EE) (EE) Server terminated with error (1). Closing log file. xinit: giving up xinit: unable to connect to X server: Connection refused xinit: server error Like I mentioned in the comments, the upgrade also changed my kernel from 3.16 to 4.9, and I just found it interesting that sudo startx shows these kernel and OS versions. My graphics card is: $ lspci -vnn | grep VGA – Vlastimil 16 hours ago 00:01.0 VGA compatible controller : Advanced Micro Devices, Inc. [AMD/ATI] Mullins [Radeon R4/R5 Graphics] [1002:9851] (rev 45) (prog-if 00 [VGA controller])