router keeps shutting off when connected too and routerlogin wont accept password

got the router second hand as used to be used for a lan connection for my quest 2 but all its been doing is just shutting off and turning back on if you connect to its wifi

also cant even log into it cause no matter what password i set for it the router login page wont accept the password and also says my serial number is wrong when i try to do a password reset

ive already tried upgrading firmware when i did have access to setting but now im just 100% locked out, using the reset button on the back doesnt work cause it still forces me to set a password that it wont accept