I find your description very confusing so could you clarify some things.

In para 1 you say "i can go online using my local area connection, however, i have to check the box stating "Obtain a ip address automatically" and " obtain a DNS server automatically" but in para 3 you also say "i can't log on to my internet once i connect my local area cable to the router."

What is the difference? Are you connecting your PC to the modem in para 1 and the router in para 3 or to the router in both?

In para 2 "It started because i changed my ip from 192.168.2.1 to 192.168.2.146 , i changed it because i was setting up a static ip address, after changing it, a toolbox pop-up and said "Ip error, Another computer is using this ip" and immediately, i was disconnected, i switched on my laptop, and changed my ip once more to 192.168.2.1 ,"

Which IP are you changing? The router, Laptop, PC or all.


What happens if you disconnect your router from the modem and connect your PC to one of the LAN ports of the router and do the following:-
1.Give the Ethernet Nic in your PC a static address of 192.168.2.150
subnet mask 255.255.255.0
2.Run the command ipconfig/all as described in "noodles" How to find an IP address in XP, assuming you use XP.

See if it gives you a "Default Gateway" IP address, if it does try logging onto the router using this address .