Oracle VM VirtualBoxが黒画面のままになりサインインできません

#概要
ひと月ぶりにVracle VM VirtualBoxでUbuntuを起動したところ、ユーザーログイン前に真っ黒の画面から進まなくなりました。特に何か変更を加えた記憶はありません。

#詳細
・Hyper-Vは切ってあります。

・マシンの設定は以下の通りです。

・以下はログの最後の数十行です。

00:00:19.121040 VMMDev: Guest Additions capability report: (0x0 -> 0x0) seamless: no, hostWindowMapping: no, graphics: no
00:00:19.121099 VMMDev: vmmDevReqHandler_HeartbeatConfigure: No change (fHeartbeatActive=false)
00:00:19.121110 VMMDev: Heartbeat flatline timer set to trigger after 4 000 000 000 ns
00:00:19.121124 GUI: UISession::sltAdditionsChange: GA state change event came, notifying listeners
00:00:19.121140 GUI: UISession::sltAdditionsChange: GA state change event came, notifying listeners
00:00:19.121434 VMMDev: Guest Log: vbg_heartbeat_init: Setting up heartbeat to trigger every 2000 milliseconds
00:00:19.121505 GUI: UISession::sltAdditionsChange: GA state really changed, notifying listeners
00:00:19.121514 GUI: UISession::sltAdditionsChange: GA state change event came, notifying listeners
00:00:19.122050 VMMDev: Guest Log: vboxguest: misc device minor 58, IRQ 20, I/O port d040, MMIO at 0x00000000f0400000 (size 0x0000000000400000)
00:00:19.440449 IEM: rdmsr(0xc001029b) -> #GP(0)
00:00:19.440466 IEM: rdmsr(0xc0010299) -> #GP(0)
00:00:19.483364 Enabling different vbva mode
00:00:19.489976 Display::i_handleDisplayResize: uScreenId=0 pvVRAM=000000000b0b0000 w=800 h=600 bpp=32 cbLine=0xC80 flags=0x1 origin=0,0
00:00:19.757592 AC97: Reset
00:00:19.757616 AC97: Mixer reset (EAID=0x809, EACS=0x9)
00:00:19.757622 AC97: Record select to left=Microphone In, right=Microphone In
00:00:19.757758 AC97: Reset
00:00:19.757763 AC97: Mixer reset (EAID=0x809, EACS=0x9)
00:00:19.757771 AC97: Record select to left=Microphone In, right=Microphone In
00:00:20.633368 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '[Line-In] DirectSound'
00:00:20.637821 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '<None>'
00:00:20.788208 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '[Line-In] DirectSound'
00:00:20.799749 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '<None>'
00:00:20.962198 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '[Line-In] DirectSound'
00:00:20.964517 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '<None>'
00:00:21.136259 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '[Line-In] DirectSound'
00:00:21.138792 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '<None>'
00:00:21.328252 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '[Line-In] DirectSound'
00:00:21.330434 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '<None>'
00:00:21.518273 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '[Line-In] DirectSound'
00:00:21.519876 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '<None>'
00:00:21.719378 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '[Line-In] DirectSound'
00:00:21.725438 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '<None>'
00:00:21.933380 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '[Line-In] DirectSound'
00:00:21.935864 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '<None>'
00:00:22.164348 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '[Line-In] DirectSound'
00:00:22.368144 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '[Mic-In] DirectSound'
00:00:22.371448 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '<None>'
00:00:22.582695 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '[Mic-In] DirectSound'
00:00:22.587398 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '<None>'
00:00:22.810695 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '[Mic-In] DirectSound'
00:00:22.812516 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '<None>'
00:00:23.043719 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '[Mic-In] DirectSound'
00:00:23.046217 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '<None>'
00:00:23.287443 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '[Mic-In] DirectSound'
00:00:23.289818 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '<None>'
00:00:23.541446 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '[Mic-In] DirectSound'
00:00:23.543294 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '<None>'
00:00:23.806699 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '[Mic-In] DirectSound'
00:00:23.809314 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '<None>'
00:00:24.084040 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '[Mic-In] DirectSound'
00:00:24.085998 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '<None>'
00:00:24.370709 Audio Mixer: Setting recording source of sink '[Recording] Microphone In' to '[Mic-In] DirectSound'
00:00:24.374137 AC97: Record select to left=Microphone In, right=Microphone In
00:00:28.814634 VMMDev: Guest Log: 03:11:36.847324 main     VBoxService 6.1.16_Ubuntu r140961 (verbosity: 0) linux.amd64 (Dec 17 2020 22:06:23) release log
00:00:28.814878 VMMDev: Guest Log: 03:11:03:11:36.847902 main     OS Product: Linux
00:00:28.815120 VMMDev: Guest Log: 03:11:36.848095 main     OS Release: 5.8.0-55-generic
00:00:28.815503 VMMDev: Guest Log: 03:11:36.848342 main     OS Version: #62~20.04.1-Ubuntu SMP Wed Jun 2 08:55:04 UTC 2021
00:00:28.816213 VMMDev: Guest Log: 03:11:36.849164 main     Executable: /usr/sbin/VBoxService
00:00:28.816395 VMMDev: Guest Log: 03:11:36.849165 main     Process ID: 616
00:00:28.818501 VMMDev: Guest Log: 03:11:36.849165 main     Pa03:11:36.851398 main     6.1.16_Ubuntu r140961 started. Verbose level = 0
00:00:28.819159 GUI: UISession::sltAdditionsChange: GA state change event came, notifying listeners
00:00:28.819548 VMMDev: Guest Log: 03:11:36.852404 main     vbglR3GuestCtrlDetectPeekGetCancelSupport: Supported (#1)
00:00:28.819586 Guest Control: GUEST_MSG_REPORT_FEATURES: 0x7, 0x8000000000000000
00:00:28.822213 GUI: UISession::sltAdditionsChange: GA state really changed, notifying listeners
00:00:28.822223 GUI: UISession::sltAdditionsChange: GA state change event came, notifying listeners
00:00:28.865839 VMMDev: Guest Log: 03:11:36.898653 automount vbsvcAutomounterMountIt: Successfully mounted 'xx' on '/media/sf_xx'
00:00:30.663043 NAT: DHCP offered IP address 10.0.2.15
00:00:30.671972 NAT: IPv6 not supported
00:00:33.942564 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '<None>'
00:00:34.246814 Audio Mixer: Setting recording source of sink '[Recording] Line In' to '[Line-In] DirectSound'
00:00:34.613623 Audio: Input for driver 'DSoundAudio' has been disabled, returning silence