D-Link DI-624 weak wireless signal

I bought used D-Link DI-624 from my friend and I set it up yesterday, but it has a very weak signal. I have 2 of 5 strenght on my laptop that is only 3m away from the router (in the same room). If I go to some other room, I lose signal. When I remove the antenna from the router, the signal strenght is the same...or I can say, it does not get any better when I connect the antenna.

What can be the reason? My friend says that it worked fine...

 

try changing the wireless setting of the router try changing the channel.