Give this a try...
I recommend doing the following:
1. Save router config to file first using IE or FF with all security add-ons disabled.
2. Factory reset the router with all other devices disconnected or turned OFF accept for 1 wired PC.
3. Reload or Update the FW using IE or FF. Just download the FW file to your local wired LAN PC.
4. Factory reset the router and then set up from scratch first and test with out loading the saved config from file.
I'd test the router out using the default IP address at first. Set up some IP address reservations for ALL devices that need to be managed by the router. Set up static IP addresses on those devcies that don't need to be managed by the ruoter. Those static IPs should be outside of the DHCP pool, not with in.
I tested this router out for a short period using 192.168.0.1 pool and didn't see any changes in IPs on my devices, reserved or static.