Tp-link tp 8960n can't access web admin

I've been using the tp 8960n ADSL router for nearly 18 months but just recently I've been enabled to log into the web admin. The IP address responds with a prompt and I type in the username & password but it just bounces back with the same box as if my details are wrong. This is strange as ever since setting up the router I've only changed the web admin password once and no one else in my family is techie enough to change it. I've tried the default password but it doesn't work either. The wireless is protected by wpa2 and has been from day one.
The router is mostly still fine although it has needed a restart once every few days to connect to devices. Has anyone encountered this before? Is it a sign that I need to replace it?

Probably been hacked. There was/is a bug with the security on some TP-Link routers that meant the password could be accessed via TFTP, decrypted then used to login and change settings.

Remote admin would have to be enabled for it to have been hacked.

The only work around is to only allow remote access from a single IP address.

The other possibility is that the config file is corrupt...

Either way a factory reset and re-configure will be needed.

I was worried about that hacking stuff. Hopefully it's just a corrupt config file though.

factory reset it and start again