Hello and welcome to justanswer, My name is ***** ***** i will be assisting you today,
I'm sorry about the issue, try the following solutions one at a time, testing the connection after each.
First let's reset the PRAM on the computer.
1) Shut down the computer.
2) While the computer is shut down, locate these keys: command (apple button), option (sometimes called alt), P, and R.
3) Turn the computer on, then press and hold Command-Option-P-R before the gray screen appears.
4) Hold these keys down until you hear the startup sound a total of 3 times.
5) Release the keys.
Next, let's try a Safe Boot. This will perform several clean up procedures that may be affecting the machine's performance and startup.
1) Shut down your computer completely.
2) Start up the computer and immediately after the startup chime, press and hold the Shift key
3) Once the gray Apple and progress indicator appear, release the Shift key
4) Note: Startup will likely take substantially longer than normal (20 - 30 minutes)
5) Shut down the computer.
Now let's check / repair the disk permissions :
1) Restart the machine.
2) Before you have opened any programs, go to Applications / Utilities / Disk Utility.
3) Run the "Repair Permissions" after selecting your Hard Drive from the list on the left.
4) Shut down the computer.
5) Plug the router and modem's power cables back in and allow them to both boot to ready.
6) Restart the computer and test your connection.
Let me know the results please