I would take one PC, one router and the one camera, factory reset router and camera. Wire LAN cable both PC and camera to router. Leave everything default on router. Check router for IP address assignment for camera. Does it get a new IP address? Can you access this IP address from the router?
Might try putting a static IP address on the PC and then check for access.
Do all of this off line from the ISP modem as you don't need that while setting up the camera.
Use IE or FF browsers to manage the router and camera. Clear any caches before starting this as well.
Disable any 3rd party firewall programs on the PC while testing this.