More details, please. Did it freeze when you tested it in the house? What kind of system is it? Are you using a 3.5" hard drive? What is the power supply and are you using some kind of voltage regulator? If so, what kind? Where is the power for the PC coming from (battery, ignition, cigarette lighter?) and how is it getting routed to the PC?
These types of things are often cause by inadequate power.