It could be a couple of things... When was the last time you did a system defrag or ran a cleaner on your machine? I would start there then reboot your system.

Once you have it powered back on see if this didn't help if not fix your problem all together. Then depending on what your machine is doing now, I would check to make sure all cables/cords are tightly connected to what they should be connected too.

If this doesn't fix it then I would call customer support of the Internet company which you are signed up with and check to see if there are any problems going on in your area and let them help you. This way they can troubleshoot whatever is the cause of the problem