Starting point for Diagnostics
If there is nothing when the key is inverted and turned, then it should be in the Ignition switch it self. Try moving the tilt wheel up and down and see if it allows the vehicle to start. If no, then replace the switch.
If however, the dash lights up, and the vehicle just does not engage the starter then look downstream from the ignition switch to the relays and the starter itself.

It it just a question of where is the break in the circuit. When the key is turned, primary voltage moves to everything waiting on the starter to engage, (Injectors, sensors, coil packs, etc). If you do not hear the injectors, and all the clicks under the hood, then double check the ignition relay that it indeed is functional and it is not the culprit. Common issue

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2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green