Repeated Crashes and Boot Errors Apparently Caused by Driver Updates

There was a typo in the second image for the EFI command:
fixoot was typed instead of fixboot

sorry it was my typo in the earlier post and should have been:
fixboot

1) open command prompt
2) diskpart
3) list disk
4) select disk 0
5) list volume
6) select volume 2
7) assign letter=U:
8) exit
9) cd /d U:\efi\microsoft\boot
10) bootrec /fixboot
11) ren bcd bcd.old
12) bcdboot c:\windows /L en-us /s U:all
13) reboot
14) diskpart
15) list disk
16) list volume
17) select volume 2
18) remove letter=U:
19) exit
20) reboot
Please use a camera to take pictures and post images into the thread for the commands and results.

I got as far as step 13 and... it booted to desktop! I assume I should go on and enter the remaining commands into administrative command prompt?

Great.
Consider the repair fragile.
1) Backup all files to another drive or to the cloud
2) Make a backup image using Macrium:
Macrium Software | Macrium Reflect Free
3) Make a brand new restore point

4) Open administrative command prompt and type or copy and paste:
5) sfc /scannow
6) dism /online /cleanup-image /scanhealth
7) dism /online /cleanup-image /restorehealth
8) chkdsk /scan
9) When these have completed > right click on the top bar or title bar of the administrative command prompt box > left click on edit then select all > right click on the top bar again > left click on edit then copy > paste into the thread

All right, I'm updating my back-ups, which may take a while. Should I still go in and remove the U: assignation?

That can be done later.
After the above steps check the drive:
Run HD Tune: http://www.hdtune.com/
Post images into the thread for the test results on these tabs:
a) Health (SMART)
b) Benchmark
c) Full error scan

Overnight run this command using administrative command prompt:
chkdsk /x /f /r C:
Use the information in this link to find the chkdsk report in the event viewer. Copy and paste > notepad > post an image into the thread.
Read Chkdsk Log in Event Viewer in Windows 10 Windows 10 Tutorials

Is it possible to create a Macrium backup image without including all my personal files (backed up elsewhere)? I have a 500 gig external drive I can use for the image, but with all my files my system is rather larger than that.

Yes that will work.
One layer or backup is fine.
Two is even better.

Is there a way to do this? My personal files are on C:, and I don't see an obvious way to disentangle those from the system files I want to image with Macrium Reflect.

To backup individual files you can copy and paste the Users folder.
That is one layer of backup.
The second layer of backup is an image or a clone.
There are two versions of Macrium.
The free edition has limited features.
What you are looking for may be available in the paid edition.
See this link: Backup and Restore with Macrium Reflect Windows 10 Tutorials
For Macrium Dalchina is an expert and he may be able to make more comments.

Microsoft Windows [Version 10.0.15063](c) 2017 Microsoft Corporation. All rights reserved.C:\windows\system32>sfc /scannowBeginning system scan. This process will take some time.Beginning verification phase of system scan.Verification 100% complete.Windows Resource Protection did not find any integrity violations.C:\windows\system32>dism /online /cleanup-image /scanhealthDeployment Image Servicing and Management toolVersion: 10.0.15063.0Image Version: 10.0.15063.0[==========================100.0%==========================] No component store corruption detected.The operation completed successfully.C:\windows\system32>dism /online /cleanup-image /restorehealthDeployment Image Servicing and Management toolVersion: 10.0.15063.0Image Version: 10.0.15063.0[==========================100.0%==========================] The restore operation completed successfully.The operation completed successfully.C:\windows\system32>chkdsk /scanThe type of the file system is NTFS.Volume label is OS.Stage 1: Examining basic file system structure ... 641024 file records processed.File verification completed. 38727 large file records processed. 0 bad file records processed.Stage 2: Examining file name linkage ... 753220 index entries processed.Index verification completed. 0 unindexed files scanned. 0 unindexed files recovered to lost and found.Stage 3: Examining security descriptors ...Security descriptor verification completed. 56099 data files processed.CHKDSK is verifying Usn Journal... 35590776 USN bytes processed.Usn Journal verification completed.Windows has scanned the file system and found no problems.No further action is required. 975633897 KB total disk space. 633450768 KB in 394885 files. 230612 KB in 56100 indexes. 0 KB in bad sectors. 797321 KB in use by the system. 65536 KB occupied by the log file. 341155196 KB available on disk. 4096 bytes in each allocation unit. 243908474 total allocation units on disk. 85288799 allocation units available on disk.C:\windows\system32>