1. Uninstall AVG.
2. Reboot.
3. Download MalwareBytes, install it, update it, perform another restart.
4. Scan the computer for any malware.
5. Go to device manager, see if there are any missing drivers, and/or conflicts (should display a warning icon next to the conflicting device.)
6. Since you are having issues with WiFi and audio, I suggest that you download those from the hardware manufacturer's website, and install them (Reboot after each driver installation.
NOTE: If the WiFi card came with the Dell computer (came from the factory - OEM), be sure to download and install the correct driver, since OEM computer manufacturers, like DELL, HP, ACER, etc., might use different hardware (especially WiFi and network cards) with the same computer models, if this is the case with your computer you will see more than 1 different WiFi card driver download on Dell's website.
The best way to determine this, is to right click on the WiFI card (from Device manager, click on Properties, go to the Details tab) and search the Hardware ID which you get for it on Google (or your favorite search engine).
In my opinion, an OS re-installation would be a better solution for the issues which you are encountering, since something have messed up your system. Even if you solve this issue without an OS re-installation, some things might come up in the near or far future with the system (like System slowdowns, Blue Screen Issues etc.). An OS-Reinstallation will solve any software conflicts/corruption, which might be present, but are not showing any symptoms (or could be that you are not noticing them, for now). Also check if you need a backup before performing the OS Re-installation.
Even if you manage to perform a System Restore, that could have been conflicts/issues which were not noticed, and they could present themselves.
Avoid AVG on this computer desktop (it's not a bad anti-virus), but it could be that one (or more) of your hardware drivers was/were conflicting with it (could be that AVG detected a false positive on one of the hardware drivers files or something else.) Or could be the bloatware which Dell have installed with the computer (and that could have been detected as a false positive with AVG, and AVG quarantined the file from the bloatware, which have caused the issue).
Could happen again, since you are using the same system setup (same hardware & same software), just doing an OS re-installation will resolve the issue for a very short period of time.
It is easier and more feasible to use a different anti-virus than replacing the system or its hardware components.