@2MuchOnMyNet 

Open the GUI of the router and see if the drive is still connected?

What OS are you one? Windows 10? Is SMB1 enabled? When you open a CMD prompt and enter NET VIEW, what happens?

Assuming you can see the drive on the GUI, do a REMOVE and then a SCAN. Does the drive show? If so, does it now work?

Otherwise, try rebooting the router. Does that fix the problem?

Lastly, take to drive to the PC and RUN CHKDSK on it, it could have a disk problem that needs to be repaired.

Do you really mean 4GB? That is small or did you mean a 4TB drive? I'll also assume it is an External Self-Powered drive, not a Portable that takes power from the USB port. Some routers have problems with portable drives.

@IrvSp Windows 10 - latest updates.  Router GUI says the drive is there (Yes, 4 TB)

CMD prompt NET VIEW gives an error 53, yet 

Drive is healthy, and like I said, it worked ONCE.  But not since.

I tried the fixes for NET VIEW -> Error 53, but no avail.  I wonder if it's a new Windows 10 "Safety Feature..."?

Tracert finds my share name but net use returns an error 53.

I dragged out an old Windows 7 machine (NET VIEW worked) - and "net use * \\<my share name here>" gives an error 53.

I checked another couple of Windows 10 machines in the house, and my unupdated work machine shows a NET VIEW, but error 53's the TP-Link shared drive.

The other machine (updated) gives error 53 for "NET VIEW".

I think there's a change in Windows 10, but it's not why my drive won't work.

BTW - ping or tracert finds the share name.

@2MuchOnMyNet

Well, I'm not about to point a finger here, as the cause is not totally clear to me.

I've got a 4TB External on an Archer A20.

I've hit the same problem.

It happens every few days... even if the drive is not used. I'm using it to stream saved DVD's to Smart TV's mostly.

Then I'll notice I can't access another computer via Windows Explorer. That PC can't access mine either.

However, I can stream off the drive, get into the router's GUI, FTP, PING the router, and in some cases use the NetBios names with NET VIEW to see the other computers.

Originally I discovered REBOOTING the router fixed it, for a few days sometimes, sometimes less than a day?

You can read my 'tale of woe' here, https://community.tp-link.com/us/home/forum/topic/249694, I think basically we have the same problem.

I did discover that if I go to the Router GUI and REMOVE the drive and then SCAN for it again, it works (NET VIEW and all sharing) until it happens again.

I've seen another similar thread here too, but it was with ARP instead.

I'd say this started about the first of the year too... could be Windows problem even, but I've Google'd and can't find anything close to this problem? Something HAS changed, but it wasn't in my router as the F/W has not been updated for a LONG TIME.

I have contacted someone from TP-Link, supplied info and it was sent to Support along with my router configuration, no feedback yet.

I have a hunch this has to do with the MASTER BROWSER operation... when a PC goes off the LAN and at night the Router becomes the Master Browser, the first PC powering up should become that. If does it seems, but it isn't getting the device list from the OLD Master, and in some cases, this IS the router. But I could be wrong too.