The reasons for your issue could be a number of things. Corruption of the router, registry errors, system infected with malware and/or virus's. It's just hard to say. Check your system for Malware and Virus's first, it can't hurt. Then clean out your registry for lost, forgotten, unused and corrupted strings.
For your router there are two more things you can try. First reset your router to factory defaults. Next would be to update the routers firmware. Just go through the tabs in the link I provided.