When you can not access 192.168.0.1

Personal opinion, if a router ever fails to allow me to log into the control pages, it receives an automatic reset to factory defaults. You can do this manually by pressing the pinhole reset button at the back of the router for more than 10 seconds. 

If you have your wifi SSID and Pre-Shared key stored somewhere that is easily accessible, reseting the router and reentering the details only takes a few minutes. If you have any suspicions regarding your usage you should consider changing both the 3825 login password and the Pre-Shared key for your wireless network.

 If you don't use the following already, you should switch to WPA2 for the Wireless Security Mode, and AES for encryption. 
Under the Wireless Basic Settings, set the Wireless Configuration to Manual so that it disables the Wi-Fi Protected Setup. 
Under Security....Firewall, checkmark SPI Firewall Protection.. Enable...as well as Block Port Scan Detection, Block IP Flood Detection, and Block Anonymous Internet Requests. 
If you don't need or use VPNs, under Security....VPN Passthrough, disable IPSec Passthrough and PPTP Passthrough.

 Lastly, Disable Remote Management and UPNP in the Administration Management page. When the changes are completed, reboot. You can then log back in and create a restoration file that will enable you to factory reset the 3825 and reload the configuration very easily. 

Under Administration....Back Up & Restore, select the Backup button to create a backup configuration file somwhere on your pc. If you ever have to reset the 3825, going back into this page and reloading the config file followed by a reboot will get you back up and running withing a couple of minutes.