As told be xpcman, you need to make sure your garage computer is equipped with wireless adapter, it could be USB or PCI wireless adapter, pretty cheap nowadays. Don't forget to install wireless adapter driver, after that you could test to connect to wireless network.
If wireless network signal is not strong, probably you could try the methods described in this article, probably can help.
you can buy a USB wireless adapter for the garage computer. If you are lucky you will have sufficient signal strength. It sounds like you have a wireless laptop. You can take it to the garage and test the signal with its software/hardware. There are USB adapters with directional antennas that might also help.