Have you tried to reboot it completely? That is, pull out the chord and waiting a few seconds before putting it back in?
If that didn't work, try going to
http://www.speedtest.net and doing the test. If the results are significantly worse than expected, you may wanna try calling your ISP (Internet Service Provider, i.e the company that you pay for the broadband) and ask them why your connection is so bad.
If your results over at speedtest.net are somewhat close to what you should expect it could be an issue with the router, I still suggest you consult your ISP's tech support and see if they can help.
Also, did this just happen randomly or has anything happened recently that could have caused it?