I'm using Homeplugs atm, seem pretty solid to me. I've never used wireless on my main machine cos i've heard of too many ppl having issues with gaming. Always hardwired til recently but the layout of my new house makes ethernet cables a bit impractical.
My advice would be follow frog's instructions and see if it helps first, and if not try
these out.
Piece o piss to set up and install, plug & play as it's supposed to be.
If you don't want to send cash straight to them,
amazon sell them at reasonable price. (note: this is a pack of 2 but they sell them individually too, you'll need one to connect to your router, and another for each PC you want to connect).