Hello!
My name is David N., and I am a Windows fan who assists others with issues in this community. I will be happy to assist you with your issue.
The symptoms you are describing point to a hard drive failure. Few things will cause a slow breakdown followed by an inaccessible boot drive. If this is the case then likely you will need a new drive and install WIndows on it to get back into the machine. Any data or applications will be gone in this event.
I recommend that you contact Lenovo support. They can help you to determine if the drive has failed and can assist with BIOS/firmware update to determine if this is the cause. Good luck
I hope this helps! Please let me know if this resolves your issue or if you require additional assistance.
Regards,
David N.