Still have the manual?
Try looking for a hole with a reset button behind it, then
turn off (unplug if you have no power strip) the modem
and the router, and push reset through the hole with a
paperclip. After that, the manual will help if you want to
secure it, but I think it should be useable if reset. It might
also be useable without resetting if you just unplug the
router and the modem, and quickly plug them back in.
(Do that while computer is off, then turn it on after a few
minutes of the modem and router being on.) If you don't
have the manual, definitely do not try the reset first
because I don't know if routers come ready to use without
setup. The router setup might be a web address in your
browser, which will be in the manual and probably need
to be done if you do reset the router.
Just do this first...
Turn off the router and modem, then turn them on again.
See if it helps.