Multiple problems regarding WD and various services (Access Denied).

I installed the FCU back on 12/2, and it went fine (had a problem with the App Store, but that's been fixed). Now I'm having a bigger problem: I can't get the Windows Search service to start. I repeatedly get this in Event Viewer:

Code:

The server {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} did not register with DCOM within the required timeout.
The Windows Search service terminated with the following error: Access is denied.
The Windows Search service terminated unexpectedly.  It has done this x time(s).

The {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} part is different in each error, and it's been doing that every 2 minutes. WHY won't it start?! I'm also having a similar problem with Windows Defender. I try to start the WinDefend service (idk why it stopped in the first place) and it stops about 6 seconds later with this appearing in Event Viewer:

Code:

The Windows Defender Antivirus Service service terminated with the following error: General access denied error

Does anyone know how to fix this? It was working fine yesterday, and I didn't install anything except an update for DAZ Studio 4 (and related products), but that doesn't usually cause problems, so it's not the culprit. If you want to know, it's legit (I've attached a screenshot of the DAZ3D product library with many orders visible on the left). As you can see, I edited out the photo and order ID for security reasons. Also, I've been having this problem since the 1st Creators Update back in April, 2017:

Code:

Definition Update for Windows Defender - KB2267602 (Definition 1.257.1417.0) - Error 0x80070643

That's been popping up every single day, whenever WD tries to download/install an update. This also happens if I try to do it manually, either through the main Windows Update screen, or using WD's built-in update window (WD->Shield button->Definition Updates).
Here's another problem I'm having:

Code:

The Background Intelligent Transfer Service service terminated with the following service-specific error: 0x8E5E0408

What on Earth does that mean? I can't do updates without that service. If I try to start it through Services, I get this:

Code:

The Background Intelligent Transfer Service service on Local Computer started and then stopped. Some services stop automatically if they are not in use by other services or programs.

It shouldn't be doing that! Also I've run SFC, DISM, and various troubleshooters with no luck.