My system, ubuntu 18.04, wanted me to perform a bios update which I did. It rebooted, tried to perform the update and then the screen went black. I've been unable to get the computer to post and even after a cmos reset nothing happens. I'm a bit lost wrt fixing this issue and I'm afraid that I might never get the computer working again. I'm using UEFI boot (legacy, I think) with an NVME ssd.
Some possible solutions, things you can do to find out what's wrong:
Get more info
Try to find out what kind of update caused these problems. Was it really a BIOS update? Or some other firmware update, e.g. for the Intel processor or SSD. Look through the firmware versions available at Lenovo. How did you install the update (from within the OS, and what OS? Is there still a copy of Windows on you pc? What happens when you turn the thing on? And has this changed after you tried things? Try to describe it as precisely as possible, e.g. do you hear the fans, do you hear beeps? Did you see anything at all on the screen? How long does it take?
What have you tried so far?
It might be that you tried more things. Have you tried booting from a CD/USB? Have you tried changing BIOS(UEFI) settings?
Try to boot Lenovo's diagnostics and other boot tools
Try Lenovo's bootable diagnostics CD, to find out if you can boot anything (this one was updated just last week!). If you don't have a cd-slot, you could try to make a bootable USB-drive with this image, but this might not work. On the downloads & support webpage for your model, there are other Diagnostics tools meant for USB-drives. But those are older than the one for CD.
Read the manual (and don't take rash decisions)
Read this P50 Hardware Maintenance manual as well as the P50 User Guide and follow all the troubleshooting steps in detail (e.g. what is your F2 key or power button is broken?). And write down every error / message you get. There's even a tool for Android that can recognize the error codes in beeps. There are many potential causes (Secure boot/unsigned drivers, RAID setups, failed driver updates. To help you, I would need to know a little more about the current state etc.
BIOS update from CD or USB
Just before submitting I discovered this: Lenovo P50 BIOS update utility. You can use the windows utility (on a different pc) to create a bootable USB to update the BIOS. On the same page, there is also a link to a bootable CD. If you can boot from a CD/USB, I'd think this is your best shot. I saw a lot of recent updates on the manufacturers website (Intel AMT, BIOS) and some of them have caused trouble. If you're not the only one: make sure to check the support community on the manufacturers website.