WORK IN PROGRESS
I did not intend this to be a write up, it is just some guidance provided to a bright mind. But, I kinda TLDRed my way into a good piece. Will edit later.
Remote diagnostic based solely on user report.
OP can stop reading now.
Please note: BIOS default settings are likely to enable the appropriate port. Nobody wants to take a call about no wifi when the coin battery ages out.
Also, BIOS IS ALMOST NEVER THE REASON for a sudden failure not reported in POST.
All reported evidence suggests a failed wifi NIC or port. BIOS is not reporting the device to Windows. There are two options in BIOS that may apply. If the NIC is USB, ensure that USB port is enabled or enable all USB ports. If the NIC is PCIe, ensure reserved PCIe port is enabled. In a consumer class laptop, these settings can be less granular. Dells typically split controls across two headings. "Onboard Devices" and "Security".
Assume user does not touch BIOS as a matter of practice or bad habit. User reports BIOS mods and/or default reset were performed only as an attempt at remedy, so BIOS is not suspect. There is a proof.
Remove ALL power/battery (ignore coin), press power button for a few seconds and then ignore device for a minute.
Re-attach all power. Detach LAN port if connected. Boot. If the DATE/TIME is correct, BIOS is not suspect.
If DATE/TIME is incorrect, failed coin battery is proved and BIOS settings are now diagnostic. Check port settings.
Any BIOS error derived from anything other than user settings or failed battery will present in POST. Boot will halt and report error condition or code to screen or provide beep error code. No video or no power-on response excepted. No video almost always indicates failed RAM. No response to power-on may indicate fault at power adapter port or failed CPU (check the brick and/or check for adapter port wiggle).
Assume BIOS settings were not user modified between last working condition and first failed condition.
Check Device Manager. Look for splat. Not all splats are bad, especially if device pre-dates Windows 10 initial release. Common to devices with fingerprint readers, IME or TPM support, or "drop protection". If there is no NIC splat, look for "Other Devices". If "Other Devices" is present, see below - Other Devices Process.
If "Other Devices" is not present AND all ports/specific port are BIOS enabled, BIOS is not reporting the device/port to Windows. Re-seat NIC. Remove, insert. Do not wiggle - common causes of poor seat include oxidization and wiggle does not remedy. Assemble sufficient to boot. Test.
If no joy, replace NIC with known good NIC. Assemble sufficient to boot. Test. If joy, problem solved.
Complete assembly and re-test.
If no joy, and card is reasonably expected to function, repeat process with a different known good NIC. If no joy, port failure is proved.
Internal port failures are VRM circuitry related. VRM circuit problems are capable of destroying all data on the storage devices, fry CPUs, fry wifi NICs, explode lithium batteries, etc.
Buy new laptop.
If purchase is not an option, grab a USB wifi thumb. Do not overspend. No need for a USB3 thumb in a USB2 port. N-class USB2 wifi thumbs are commonly less than $20.
For the interested parties, the above detail illustrates why drivers are not suspect in this case. There is no splat, there is no unknown device. Windows does not know the device is there.
Don't See Device = Don't Need Driver.
Other Devices Process
If "Other Devices" is present, select each listed device. These are 'unknown devices'. For each unknown device, double-click to open Properties. Select Details tab. Drop down list and select Hardware ID. It does not matter which drop down entry you select. The shortest is sufficient. Right click VID###x&PID###x and choose Copy.
Open browser. Paste (not paste and go). Remove leading "USB/" if present Not all search engines handle the leading "USB/" gracefully. We only need complete VID & PID (Vendor ID and Product ID). Search. This will reveal the identity of the unknown device. For whatever reason, product support is not canned in Windows. Not an uncommon thing. Locate driver from reputable source, Sometimes, you have to go all the way to the chip maker. Common with RealTek devices. RealTek makes the chips on many NICs (and audio devices).
CAUTION: The google return on a search for VID&PID is a list that contains some VERY nasty sources. Keyloggers, IP redirects, payloads. Very Bad Things. Drivers communicate DIRECTLY with the device in assembly language from the kernel. Devices with buffers (such as NICs) provide a storage location for ill code. It is possible to create a worm at a level below the HAL. The worm will communicate in machine code directly to the CPU. Ask Iran if they enjoyed StuxNet.
Remember, a CPU is just a form of software in a hardwired configuration. A CPU is hackable from the bus. See Spectre MeltDown.
Do not trust anything there if the domain is not recognized as a trusted source. You WILL encounter some underhanded marketing techniques. Just Say No. You are looking for a driver and drivers are free. Driver install does not require any software not contained in the driver release. Included here is a link to Device Hunt. Provided as a tool for locating obscure drivers.
Driver Manager software is problematic. I won't TLDR you on this point. The knowledge contained herein is sufficient to negate the need for toys.
RELAX: Devices built for WinH8 and WindX are likely to appear at the top of the list, branded, and from a trusted domain. There are a handful of valid reasons why driver support is not canned. Those reasons include device was made for WinH8 and the manufacturer chose not to fund WindX support migration. If you can't find a wifi driver for your device model, identify a more current model that uses the same chip AND has WindX support and use that driver. It is 100% compatible.
Doug Thwaites repository interface
USB PID repository