I work in IT (Infrastructure). As djr8369 points out the PC can't see the main drive. Definitely worth double checking the drive is connected properly, checking BIOS can see it etc. Also check the boot type as Legacy and UEFI work differently.
If it's a HDD you can run some repair routines on the boot sector but these are hit and miss as to whether they work. The good news is any data will still be on there and can be obtained by plugging in as a secondary drive with a different boot drive or via another computer. However, if it's an SSD which a lot of modern PCs have, the data is lost due to the boot partition hold the database as to where the files are stored.
You might get lucky with doing a repair with a Windows DVD but I wouldn't get your hopes up.
Also, if the error is on an SSD I would recommend buying a new one and putting Windows on as there is more than likely some corruption on the SSD.