Before installing a third-party firmware, you should have
first ensured that you have the installation media for the router's original
firmware from the manufacturer, and also that you master the know how, or have the tools, to force its installation in a bricked router, just in case.
If the installed firmware was DD-WRT, its default username is root and default password is admin.
If these do not work, do a hard reset and try again.
If this does not work, reinstall your original firmware.
Assuming your router is the TL-WR740N V5, you can download its firmware
and installation utility from the TP-Link Support site.
If your router is not the V5, search for it in the TP-Link site.
In the case that this also fails, and as you can access the SSH,
you can use the firmware and instructions found
in the page TP-Link stripped firmware.
Even if this revives your router, I would still reinstall over it
the firmware downloaded from TP-Link, just to be sure.
ERR_CONNECTION_REFUSED
indicates your router is refusing the connection. This means the firmware you installed doesn't appear to have a web configuration enabled. I strongly suggest you SSH into the device, upload the default stock firmware, and restart the process of moving to WRT – Ramhound – 2017-05-08T19:14:17.837What firmware did you installed? Have you tried accessing your router via telnet (port 23) or SSH port 22)? – Alex – 2017-05-08T19:16:27.470
@Alex I can now access through SSH using PUTTY but I cant seem to find working command for enabling web GUI. – hacker red – 2017-05-08T19:25:51.603
@Alex name of firmware "openwrt-ar71xx-generic-tl-wr740n-v4-squashfs-factory" – hacker red – 2017-05-08T19:26:09.233
Here is a good tutorial on how to install a webGUI: https://wiki.openwrt.org/doc/howto/luci.essentials# however I think you should follow @Ramhound's advice and start over.
– Alex – 2017-05-08T19:31:56.277@hackerred - The firmware you loaded doesn't have luci installed which is the reason the connection is being refused. – Ramhound – 2017-05-08T19:42:09.023