@dandyy11 welcome to WiredPakistan.
before the router, how was your PC set with the CPE? means how have you been in use with your PC and your Wateen's CPE?
was your PC obtaining IP automatically from the Wateen's CPE. OR your PC was set to an IP manually. you would need to see it in your PC's TCP/IP settings.
normally it is set with "Obtain IP automatically". so the following is the process if you were previously set automatically.
1- if you have touched the settings in your Router then restore it to factory settings. (by default it is set to get IP automatically and DHCP enabled.),
2- take the ethernet cable out from the PC that is coming from the CPE. you will use it in step 6.
3- another ethernet cable, take it FROM one of ethernet ports in Router labeled (1,2,3,4 but not from the internet port) TO your PC's ethernet port.
4- set your PC (in TCP/IP settings) to obtain IP automatically from the router that you have just connected in step 3. if it is not getting IP or warning about limited connectivity, then try re-connecting or disabling/enabling the connection.
5- consult your user manual* of the Router and login to its web interface. the first page you will get where you can make sure your router is already set to obtain IP automatically. if it is not then set it to "Obtain an IP automatically".
6- now take the ethernet cable (that you have taken out from PC in step 2) and put it in the Router's internet port.
all's done. your internet should work now. and your connections should look like below
----> Router(192.168.15.2/255.255.255.0/192.168.15.1) assigned by the CPE
(192.168.1.1) Router Local IP
-------> PC/Laptop (192.168.1.100/255.255.255.0/192.168.1.1) assigned by router.
and if you have previously used to manually set the IP on your PC when with Wateen's CPE, then in above step 5, try setting the IP manually on the router's web interface.
ethernet cables used in the process must be Straight-Through.
after configuring the Internet correctly as above you can freely proceed to configure wireless security to connect wirelessly. however it doesn't require the above things to be set before you use the router wirelessly if every thing is on factory defaults.
(If using latest wireless card specific driver/software on the PC/Laptop)
Just turn on the Router and you should see it in your PC, that a wireless device is in range. connecting to this router very first time, will prompt you to enter the Device ID*. enter the device id and you will be connected to the Router wirelessly. the Device Id is asked only if your router's wireless settings are not configured already and your PC doesn't have any profile already created for this router.
this wireless configuration can be set again as per your desires after you are connected with the router and have access to its web interface.
when you connect wirelessly via the Device ID, then actually the router configures itself as WPA security. you need not to change the configuration again but if you want any other security settings you will do it through its web interface. you will also need to re-set the profile in your PC/Laptop
(If using windows to handle wireless connectivity instead of a driver software)
still you can connect with a new router by setting in the Wireless Connection Properties > Wireless Network tab, using security as Open and Encryption disabled.
however the better approach is to configure your router via ethernet connection and then configure the wireless security.
I hope it would help.
*Router's user manual http://downloads.linksysbycisco.com/downloads/BEFW11S4-v4_ug,0.pdf
*Device ID can be found on the bottom of your Router, some what near to the serial number.