Double check that all of the cables, wires and hardware are fully seated.
Did you bring all of your hardware with you to your relative's house?
- Monitor and video cable?
- Keybord? Mouse?
- PSU AC power cable?
- USB devices?
Have you tried using a different electrical outlet in another room in your house?
Is the PSU cable plugged into an electrical strip or UPS?
Are there any USB devices connected to your system that weren't connected at the other house?
Have you tried booting with your graphics card installed in a different pci-e slot?
See if your bios has a Gen2 option for your video card and see if this "fixes" the boot problem.
How old is your power supply?
Normally I would suggest trying a different power supply, but you said that you didn't have any problems at your relative's house.