Power diwn
macbook pro powers up then down again after a few seconds either plugged in or by battery but stays on if you keep any button oressed down
MacBook Pro
- Try resetting the SMC and NVRAM/PRAM
Intel-based Macs: Resetting the System Management Controller (SMC)
- Try starting in Safe Mode
OS X: What is Safe Boot, Safe Mode?
- Boot to Recovery and repair the startup disk
OS X: About OS X Recovery - Apple Support
- If it is repairable reinstall the OSX
How to reinstall OS X on your Mac - Apple Support
- If you do not have a backup use disk utility to restore the internal disk to an external disk so you can try to recover data.