My Lenovo Yoga 9 14ITL5 when starting goes to the Screen "select booting device" there i have the Options 

-Windows Boot Manager (nothing Happens If selected)

-setup (i can Access and make Changes but AS soon as i leave im Back at the select Boot device Menü)

-diagnostic Splash (black Screen showing some information about the build in Hardware) 

What can i do?

Hi guest22912,

I'm sorry about your Lenovo Yoga 9 14ITL5. It sounds like your laptop is having trouble booting up. Here are a few steps you can try:

1. Reset your BIOS settings to default. You can do this by entering the setup option you mentioned, then look for an option to reset all settings to default. Save and exit, then try booting up again.

2. Check your hard drive's health. You can do this by selecting the diagnostic splash option. If there are any issues with your hard drive, it might be the reason why your laptop can't boot up.

3. Try booting up in Safe Mode. Restart your laptop and press Fn + power > system recovery > troubleshoot > start up settings. You also do F8 repeatedly until the Advanced Boot Options menu appears. Select Safe Mode and press Enter.

If none of these steps work, it might be best to contact a Lenovo support specialist for further assistance. You can do so by following this link.

I hope this helps. Let me know if you have any other questions.

Best regards,

Diox_Lenovo