Hi, I am totally new to computers and don't know much about them so I need some help.
My brother came back for a month then left, but he connected a wireless router so that we could both use the internet, however since he already left and I am the only one who uses the computer I was trying to unconnect the wireless since my internet it not as fast as it used to be. I tried to do this and reconnected all the cables, but I can't connect online. I know there's a connection because whenever I reattach the cables it says internet connection found but I can't seem to access the internet. Have any ideas why?

What kinda of internet connection do you have? DSL or cable?

If you have DSL, you may need to install a piece of software that will log you in to PPPoE.

I'd call your internet provider's support line. They will usually help you get set up using a single computer.

Some more information is needed here.

What sort of an internet connection do you have? What did you disconnect/reconnect where?

Most likely your computer was set to static IP configuration while your intrenet connection needs a dynamic address setup.

I have a cable modem. I just rehooked the wires from the netgear wireless router back into the linksys cable modem and then into my computer. What is a dynamic address set-up? Sorry, do not know much about computers.

Look in the documentation for your netgear router, there should be a way to turn wireless off in the router if you no longer want it to broadcast its signal.

If you are removing the router completely, try powering the cable modem off for about 5 minutes before connecting your computer to it, then reboot your computer. This fixes lots of problems when switching from one network device to another on caable modems.
Also, to check to see if your IP is static, go to Network Connections, right click the Local Area Connection, go to properties, look for Internet Protocol (TCP/IP), click it, click the properties button, it will either have a tick in "obatin IP automatically" or Use the following IP". You'll want to select automatic.