My friend, Does your pc have wireless capability? You don't say whether yours is a lap top PC or a larger desk top PC. Not all computers come with wireless capability. You say it works downstairs on a eithernet cable but you don't say if it works wirelessly at that location.
My friend, wireless is convenient, like fast food. However, wire is a better method of constructing a network for many reasons. Wired is like that meal you have on Sunday Aftenoon with the roast with all the trimmings.
Wireless runs at 10 and is not always secure. Wire runs at 100 or 1000, is secure and simple to configure. It is not normally interfered with by other wireless influences transient or intransient.
So, what to do: Run some Cat 5e through the cold air return from the upstairs to the downstairs. If you need multiple outlets up stairs, add another switch, wireless or wire. I recommend LinkSys products because I have had the best success with that brand. Of course there are many others including D-link and NetGear to cite but two.
I also recommend Network Magic from Cisco. Free to download and evaluate for 7 days, NM will help setup your network, establish security you are comfortable with and will also help you share resources on your network. Following the eval period, Cisco will allow you to continue to use the program though with some features not working. If you can live without those features, no problem. For myself, I liked the product so much I use the paid professional version. Find it at http://www.purenetworks.com/nmlp/home-networking.php?gclid=CLrq2Y2q9J4CFcx25QodZ1-4JQ&src=google&kw=network+magic+download
If you really want wireless and your computers are not wireless ready, you can get wireless adapters for most computers at the 'big box' store in your area. Around my area, more specifically, we call the 'big box' Staples, Office Max, Office Depot, and Best Buy. There are others, of course. You may also find what you need at a FixYa.com advertiser or partner or the smaller box, Radio Shack. FixYa.com does not sell products at this time.
I hope these comments help you resolve your network issues. If you require more information, post a comment to this question.
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