Q: My 2001 BMW X5 won't start. I think it is due to power loss

Hello, the first questions to answer are "Are any problem codes set? Is your Check Engine light on?". Based on your observation of "no power", and your extended mileage, there are several problems likely that would result in "no power": your timing chain or valve timing components could be worn enough to affect timing and power. The catalytic converter could be clogged from lots of miles, and long term contamination. You don’t mention a misfire or overheating, but a blown head gasket could cause a no power situation, as well as worn piston rings. I would recommend having a Car Is Not Starting Inspection completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose this problem, get an accurate assessment of damage and cost estimate for repairs.