i would check your connections to the display, make sure they are not corroded.
Check the ground as well.
Make sure you do not have any blown fuses in the fuse box.

the fact that it does start and run for 30secs and then shuts down does tell me that the oil pressure switch may be bad. If the engine looses oil pressure it will shut the engine down after a short bit.
check the continuity at the oil pressure switch and make sure it is functioning properly.