According to this reference guide, a 2,2 code indicates a Motherboard: Power Supply issue. Since you indicated that you move the components to a new case I would check to make sure your power supply connections are properly made. In addition, I would check the mounting of your motherboard to make sure the mounting screws and standoffs are not shorting something on your motherboard. Make sure there are no additional standoffs only the ones corresponding to mounting holes on the motherboard. Although this would be a lot of work, you could remove the motherboard and power supply and try running it outside the case.

How did you wire the front panel in the new case since Dell uses customized connections from motherboards to front panels in their cases?

You could try resetting BIOS to see if that clears the error code:

1. Power off, unplug
2. Press/hold power button for ~15 sec
3. Open case and remove motherboard battery (check Service Manual for details)
4. Press/hold power button for ~30 sec
5. Reinstall the battery (Time for fresh CR2032 3-volt coin cell battery? ~$2)
6. Close up and connect mouse, monitor and keyboard
7. Reboot