HP Pavilion Dv5000 “Operating System Not Found” after replacing fan

Had the fan replaced (it was buzzing) in an HP Dv5000 yesterday. Brought the unit home, it booted & ran fine last night. This morning on powerup, get “Operating System Not Found” message! Is it possible the technicians jiggled something in the laptop that caused this? It’s very coincidental that this happened after a repair. Many important files on this laptop–ideas asap would really be appreciated! Thanks!