Does your house work completely with an ethernet cable or do you have a router that everyone in the house uses? (since you mentioned the other two computers use wi-fi)
And does your cable connect to the router?
If you do use a router, there may be communication problems between it and your computer. If that's the case, you'll have to fix that by "restarting" the router communications through it's website that you have to sign into (at least this is the case with NetLink)
For now, try cleaning up your computer. Always nice to do that
Defrag and all that. Are you using Windows 7/XP/Vista?