1) Power everything off, including the Cable Modem. The modem should be left without power for a couple of minutes - this is important so that the modem releases the association between your existing network connection and the IP address it allocates. It will detect a new network device and allocate a new IP address.
2) Connect the Router's WAN (Internet) Port to the Cable Modem's ethernet port with a straight-wired network cable.
3) Connect the PC's network adapter to one of the Router's LAN ports with a straight-wired network cable.
4) Power on the Cable Modem and wait for it to boot fully with 4 lights on. Power on the Router and wait for it to boot fully and indicate that it is online. Finally boot the PC.
The PC *should* get an IP address automatically from the Router. If the Router's address is 192.168.0.1 then the PC should get an address in the same range. If it is unable to get its IP address from the Router, Windows will allocate a default address in the 169.254.x.x range, which will give you a "Limited or No Connectivity" indication and you won't be able to access the Router or get online. If this happens, try giving the PC's Local Area connection fixed addresses:
IP address 192.168.0.5
Subnet Mask 255.255.255.0
Default Gateway 192.168.0.1 (the Router's IP address)
DNS Server address 192.168.0.1 (the Router's IP address)
Now open your web browser and enter the router's IP address - 192.168.0.1 - which should open its Setup pages. If, after resetting it, it is still password protected, the router must have a default password and you will have to find out what that is. Did you get a manual or CD with a manual in PDF format with it?