If your computer connects to other wireless networks, and you have verified that you have the correct frequencies, then more than likely it is not a hardware issue.
Many times when your internet has intermittent issues, but you are still connected to the network, or if you are connected to the network, but not to the internet, you have a DNS server problem.
If so, then there might be a problem in your settings on the problem computer. It could be a lot of things, but interference and DNS problems are the most common in home networks.
Are you connected to the network, but just not able to access the internet? One of the first steps in troubleshooting a network connection problem is figuring out if you have a valid IP address, and if it was configured automatically or manually.
Find "Internet Protocol Version 4 (TCP/IPv4)", click it, and then click "Properties." Then click "Obtain and IP address automatically". Find your network adapter and right click it, click properties, go to "Internet Protocol (TCP/IP)" and click "Properties". If you want to obtain your DNS servers automatically, you can change those as well.
If your router is an A router, then you need to get a wireless NIC that supports 2.4 and 5 GHz networks.Due to a recent demand for help with home networks, I have decided to write this instructable on how to troubleshoot your home network.If you are not already familiar with the basics of how your network works, I suggest reading my previous instructable "How your home network works".The IPv4 address should be on the same subnet (see below).Now we need to check and make sure you are on the correct subnet.