Laptop stuck in BOotmgr missing

[magicniner]

What make and model? The keys to force different bios options vary with BIOS type.

Most laptops from the last 10 to 15 years come set to boot from in order of priority, if present - USB, CD, HDD

Remove the HDD and see what it does, you should at least be able to access BIOS without the system trying to boot from a potentially corrupt drive. HP Compaq have drive test utilities in the BIOS to check for hard errors.

Clean build of Windows? Dell will usually have a hidden recovery partition with the install media, others vary.
If your initial build had separate OS and data partitions you can rebuild Windows without data loss, if not you could put the drive in a cheap USB enclosure and use another PC to retrieve data (and test HDD integrity) before trying a build,

- Nick