I have followed the advise in other thread to reset my router, but the password from the back of my router for admin interface is not working! (I want to set up a file share on local network, and I need to reserve the IP address for my machine to do that)

I have also had other issue where router becomes unresponsive after few days of working, i.e. I can connect to it with cable or wifi, but the internet is inaccessible and so is the admin page at the 192.158.2.254.

My router is labeled as KPN Box 12 on the back.