Drivers marked as unsigned in Windows 7

I have a problem with my Windows 7 Professional 64-bit laptop. I rebooted a few days ago and the system would not start. I received this BSOD:

c000021a The session manager failed to create protected prefixes System process terminated unexpectedly with a status of 0xc000003a

I could not boot into any Safe Mode or Command Prompt. But when I selected Disable Driver Signature Enforcement, I could boot into Windows.

Once in Windows, I opened a command prompt and ran SIGVERIF. This listed 39 driver files that it thought were not signed. I am not sure about this, because I performed a binary file compare (FC /B) on a couple of the files against a fresh install of Windows 7. Specifically, drivers BATT.DLL and MMCICO.DLL were identical.

This is what I have tried:

• ran a full Sophos anti-virus scan with latest virus catalog (no issues detected)
• uninstalled any Windows Updates that were applied between the last successful boot (5/10/2018) and the failed boot (15/11/2018). These were KB4457144, KB2952664, KB4457038.
• uninstalled any software that was installed between the last successful boot and the failed boot.
• applied KB4467107 and rebooted.
• applied KB4457918 and rebooted.

But the system still gets the BSOD and will only boot when I select the Disable Driver Signing Verification boot option.

Is this a fault with whatever Windows uses to determine whether a driver is signed or not? Or is this a problem with the driver files themselves becoming corrupted?

Any assistance and suggestions welcome.

The 39 driver files that SIGVERIF flags as unsigned are:

batt.dll
mmcico.dll
agilevpn.sys
asyncmac.sys
blbdrive.sys
cmbatt.sys
compositebus.sys
discache.sys
hdaudbus.sys
i8042prt.sys
lltdio.sys
monitor.sys
mskssrv.sys
mspclock.sys
mspqm.sys
mstee.sys
ndisuio.sys
ndiswan.sys
rasl2tp.sys
raspppoe.sys
raspptp.sys
rassstp.sys
rdpbus.sys
rdpcdd.sys
rdpencdd.sys
rdprefmp.sys
rspndr.sys
serenum.sys
serial.sys
sermouse.sys
tap0901.sys
tpm.sys
tunnel.sys
umbus.sys
vga.sys
vwifibus.sys
vwififlt.sys
vwifimp.sys
wfplwf.sys