1 - When you say "it" turns on for a second, are you talking about the PC or the DSATX?
2 - How it it wired? Including wire gages and what sources you tap into.
3 - Did it work before your car went into the shop?
4 - Does the PC work with a regular ATX power supply in the house?
Simply posting "I put it in and it don't work" provides absolutely no information with which to troubleshoot.