DeskJet 3720 prints test pages from printer, but prints blank pages from PCs

[IndyJonesX]

I have a HP DeskJet 3720 All In One. I hadn't used it for a while but it used to work fine. It is connected via USB.

The problem:

Despite being able to clearly demonstrate that it has ink, when instructed to print from either of my PCs, the printer prints blank pages. It outputs the correct number of pages, and it appears to be moving as required to print the text and images in the documents that were sent to it. But it simply creates blank pages.

To be clear, this is not an ink issue. The printer proves this, because if I use:

• The printer hardware itself:
  • The Info button test gives me a printed page of "Printer Information Page". Much black text.
  • The Cancel button test gives me a printed page of "Printer Status Report".Much black text.
  • The Wifi + Info button test gives 3 mostly blank pages, with a few little blue icons spaced apart on them.
• The HP SMART application:
  • The Demo Page test, gives me the printed demo page titled "HP DeskJet 3700 All-in-One Series" with the image of the printer and all its upselling blurb. 
    • From other tests, I know that this is simply an internal page that the printer is getting from its own memory, not from the PC's data. I can't remember exactly which internal printer test prints the demo page (too many tests), but it's one of them in there.
• The HP PRINT AND SCAN DOCTOR application: 
  • The first Test Print option after instructing it to fix printer problems gives a blank page.
  • The second Test Print option after telling it to try an internal test print, I get a printed page with some colours and shapes and what not. It has a little emblem that says "Faster drying, Bolder blacks, Vivid colours". It makes sense that this works, because it has said that it was an internal test. It's not printing something that the PC had transmitted to it.
• The HP DJ 3700 SERIES TOOLBOX application:
  • The Align Cartridges test, for example, gives a printed page full of black and white lines and bars and dots in numbered rows and columns. Ie., it's exactly what an alignment test should look like.

But, if I use: 

• Either of my PCs (both Windows 10) to print anything from Chrome, it goes through all the motions of printing perfectly, including the print head moving around like it's doing something, then produces completely blank pages. 
  • Likewise for trying to print from Notepad++. Blank pages after going through all the motions.

According to the printed test page, and the umpteen different places in the HP software that say this, ink levels are K - Low, CMY - Ready.

HP Print and Scan Doctor 5.7.4 shows nothing wrong with the printer. All 9 icons: 

 - Recommended Updates

 - Print Spooler

 - Driver check

 - Device Status

 - Device Manager

 - Device Online

 - Print Queue

 - Port Match 

 - Device Conflicts

... have a green tick. From there, if I click Test Print, I again get a blank page.

When telling HP Print and Scan Doctor 5.7.4 to fix the scanner, it shows there to be a driver problem. I have to tell it to skip that issue for it to complete the rest of the scanner checks, which it does. The other icons are all green ticks. 

• And yet, scanning does actually work fine. I've been using it tonight.

Wi-Fi Stuff

I will add that nothing to do with Wi-Fi connectivity has appeared to work. Everything described in this post is using a USB connection.

• The HP Print Service Plugin on my Android phone simply never discovers the printer
• HP Smart says Wireless is on but not connected
• The printer's little blue light on the Wi-Fi button is flashing
• Microsoft Windows Firewall is Disabled in HP Print and Scan Doctor. (I disabled it.)
• Somewhere in all these applications is an option to convert the printer's connection to the PC from a USB connection, to a Wi-Fi connection. When I do this, simply no Wi-Fi networks in my house appear, not 2.4Ghz (we have 2 networks), not 5Ghz (another 2 networks), not any neighbours', none. I tried typing in the names manually but no luck.
  • I can't remember which of the different HP application had this setting. 

I've tried reinstalling drivers with the website downloads with the PC reboots and printer power unpluggings that has required. On my second PC, this was the first time the printer has even touched it, so it definitely wasn't a case of old drivers doing anything.

tl;dr 

1. The printer can physically print just fine. Black and white, and colour. Things printed from the printer's memory print successfully. 
2. Things printed from both an old and new PC go through the motions, but only "print" blank pages.
   • The printer is demonstrably aware of how many pages it was told to print. It always spits out the right number of blank pages.
   • By the looks of the head's motion, it also seems to know exactly what data to print. It goes through the motions, it simply does not put the ink on the paper. So data is getting through to the printer.
3. Anything to do with Wi-Fi simply doesn't work. I don't really care about this, USB connectivity is fine.
4. Print and Scan Doctor says the scanner has driver issues, yet it works. And says the printer does not have driver issues, yet it doesn't work.

Googling anything that tries to mention "blank pages" returns nothing but stories about ink. This is not a story about ink. The ink works.

That's what makes this frustrating, because even if I go and buy new ink, I know I'd just be giving more money to HP for a printer that doesn't print even when it clearly demonstrates having the ink to print with.

Hoping this is a known issue, but it's very hard to find info on amid all the ink stories.