Has this PC previously been connected by ethernet to your "house wifi"? If not, I suggest that you do this and the IP address may be rectified. If it doesn't then there may be a Winsock Error - this may be rectified by resetting the TCP/IP stack and resetting the Winsock. You do not say which OS you are using.
You need to get the command prompt (Windows 7 type in CMD), XP start, run, type in CMD.
You will then get the black box.
netsh int ip reset resetlog.txt
If this does not work get the command prompt again and type in
netsh winsock reset catalog
It sounds as if you will need some sort of booster/repeater - daisy chaining another router often works. Another consideration is the use of a Home Plug if your outside office is on the same electrical circuit as the house. Most people use these with an ethernet connection but wireless ones are available but usually cost more. Have a read of this article, it may help.