what causes a HP COMPAQ DC5700 NON-SYSTEM disk or disk error after starting it

[Hotnmad2]

My husband ordered a used, not refurbished HP Compaq DC5700 Windows 7 Desktop PC from Ebay, the seller states it was tested and ran great! Well guess what? It won't start. A black screen states there's a "Non-System Disc or Disc Error Replace Strike any key, it won't let him open or install anything to fix it , ok what exactly does that mean? Did it come this way and the seller wanted free cash for his broken pc? damaged in 7 days of transit?

 

[Emerald]

It could mean that the system does not recognize the HDD or that there is no OS installed.

Check the BIOS and see if the HDD is recognized by the system.

boot of a Linux Live CD and check if a OS is installed.