1) hard drive failure,
2) software issue with Windows
Please provide the exact error message.
In the meantime, obtain Memtest (.org), boot to it and run for at least an hour to test your RAM.
As well, try to obtain diagnostic, boot software from your hard drive manufacturer and test the hard drive.
*You can change the BOOT order in the BIOS. If you only have the hard drive selected then you can not boot from USB or CD/DVD.
Recommended boot order:
3. Hard drive
(The BIOS checks USB first to see if any boot devices exist such as a diagnostic USB utility or Linux. It then repeats for the CD/DVD drive if it found nothing on USB. Finally, if nothing is found on either it boots to the hard drive which should be Windows.)