I would suggest that the first thing you do is unplug the router and reconnect after 5 minutes. This will reboot the router. Then boot your computer once the router has all three green lights on or flashing. Your problem is obviously aquiring a network address and this may fix it.
Then Double click the green D in the taskbar tray. This will open the D-Link User Interface. Click on Site Survey and your connection should be in the top pane "Available Network". You need to add it to the Profile Pane below and make sure it`s at the top of the list by highlighting it and using the arrows to the right to move it up the list. (Above default connection if it is listed)
If you have encryption you will need to put the key into the profile when you add it to the list.
You need to check if your brother had access to the router settings and if he changed any of them since the uptime is 49 hours would suggest that the router was rebooted then.